diff --git a/app/actions/local/post.ts b/app/actions/local/post.ts
index 8dffef59988..5a9b159a747 100644
--- a/app/actions/local/post.ts
+++ b/app/actions/local/post.ts
@@ -160,7 +160,7 @@ export async function markPostAsDeleted(serverUrl: string, post: Post, prepareRe
             p.message = '';
             p.messageSource = '';
             p.metadata = null;
-            p.props = undefined;
+            p.props = null;
         });
 
         if (!prepareRecordsOnly) {
diff --git a/app/actions/remote/post.ts b/app/actions/remote/post.ts
index e358a094cb8..fd3193178d6 100644
--- a/app/actions/remote/post.ts
+++ b/app/actions/remote/post.ts
@@ -80,7 +80,7 @@ export async function createPost(serverUrl: string, post: Partial<Post>, files:
     const pendingPostId = post.pending_post_id || `${currentUserId}:${timestamp}`;
 
     const existing = await getPostById(database, pendingPostId);
-    if (existing && !existing.props.failed) {
+    if (existing && !existing.props?.failed) {
         return {data: false};
     }
 
@@ -240,7 +240,7 @@ export const retryFailedPost = async (serverUrl: string, post: PostModel) => {
         // timestamps will remain the same as the initial attempt for createAt
         // but updateAt will be use for the optimistic post UI
         post.prepareUpdate((p) => {
-            p.props = newPost.props;
+            p.props = newPost.props || null;
             p.updateAt = timestamp;
         });
         await operator.batchRecords([post], 'retryFailedPost - first update');
diff --git a/app/actions/remote/search.ts b/app/actions/remote/search.ts
index 7f99bb6e945..2a5783eacda 100644
--- a/app/actions/remote/search.ts
+++ b/app/actions/remote/search.ts
@@ -161,7 +161,7 @@ export const searchFiles = async (serverUrl: string, teamId: string, params: Fil
         }, {});
         files.forEach((f) => {
             if (f.post_id) {
-                f.postProps = idToPost[f.post_id]?.props;
+                f.postProps = idToPost[f.post_id]?.props || {};
             }
         });
         return {files, channels};
diff --git a/app/components/files/files.tsx b/app/components/files/files.tsx
index da11d676f2d..710466ea79e 100644
--- a/app/components/files/files.tsx
+++ b/app/components/files/files.tsx
@@ -24,7 +24,7 @@ type FilesProps = {
     location: string;
     isReplyPost: boolean;
     postId: string;
-    postProps: Record<string, any>;
+    postProps: Record<string, unknown>;
     publicLinkEnabled: boolean;
 }
 
diff --git a/app/components/markdown/channel_mention/channel_mention.tsx b/app/components/markdown/channel_mention/channel_mention.tsx
index 5dceb752f62..554dfbf1bf5 100644
--- a/app/components/markdown/channel_mention/channel_mention.tsx
+++ b/app/components/markdown/channel_mention/channel_mention.tsx
@@ -10,12 +10,38 @@ import {useServerUrl} from '@context/server';
 import {t} from '@i18n';
 import {alertErrorWithFallback} from '@utils/draft';
 import {preventDoubleTap} from '@utils/tap';
-import {secureGetFromRecord} from '@utils/types';
+import {secureGetFromRecord, isRecordOf} from '@utils/types';
 
 import type ChannelModel from '@typings/database/models/servers/channel';
 import type TeamModel from '@typings/database/models/servers/team';
 
-export type ChannelMentions = Record<string, {id?: string; display_name: string; name?: string; team_name: string}>;
+export type ChannelMentions = Record<string, {id?: string; display_name: string; name?: string; team_name?: string}>;
+
+export function isChannelMentions(v: unknown): v is ChannelMentions {
+    return isRecordOf(v, (e) => {
+        if (typeof e !== 'object' || !e) {
+            return false;
+        }
+
+        if (!('display_name' in e) || typeof e.display_name !== 'string') {
+            return false;
+        }
+
+        if ('team_name' in e && typeof e.team_name !== 'string') {
+            return false;
+        }
+
+        if ('id' in e && typeof e.id !== 'string') {
+            return false;
+        }
+
+        if ('name' in e && typeof e.name !== 'string') {
+            return false;
+        }
+
+        return true;
+    });
+}
 
 type ChannelMentionProps = {
     channelMentions?: ChannelMentions;
diff --git a/app/components/markdown/channel_mention/index.ts b/app/components/markdown/channel_mention/index.ts
index 6843061f79e..7e56b7f4800 100644
--- a/app/components/markdown/channel_mention/index.ts
+++ b/app/components/markdown/channel_mention/index.ts
@@ -12,8 +12,6 @@ import ChannelMention from './channel_mention';
 
 import type {WithDatabaseArgs} from '@typings/database/database';
 
-export type ChannelMentions = Record<string, {id?: string; display_name: string; name?: string; team_name: string}>;
-
 const enhance = withObservables([], ({database}: WithDatabaseArgs) => {
     const currentTeamId = observeCurrentTeamId(database);
     const channels = currentTeamId.pipe(
diff --git a/app/components/markdown/markdown.tsx b/app/components/markdown/markdown.tsx
index 934e7cdfb01..369c435a222 100644
--- a/app/components/markdown/markdown.tsx
+++ b/app/components/markdown/markdown.tsx
@@ -17,7 +17,7 @@ import {typography} from '@utils/typography';
 import {getScheme} from '@utils/url';
 
 import AtMention from './at_mention';
-import ChannelMention, {type ChannelMentions} from './channel_mention';
+import ChannelMention from './channel_mention';
 import Hashtag from './hashtag';
 import MarkdownBlockQuote from './markdown_block_quote';
 import MarkdownCodeBlock from './markdown_code_block';
@@ -33,6 +33,7 @@ import MarkdownTableImage from './markdown_table_image';
 import MarkdownTableRow, {type MarkdownTableRowProps} from './markdown_table_row';
 import {addListItemIndices, combineTextNodes, highlightMentions, highlightWithoutNotification, highlightSearchPatterns, parseTaskLists, pullOutImages} from './transform';
 
+import type {ChannelMentions} from './channel_mention/channel_mention';
 import type {
     MarkdownAtMentionRenderer, MarkdownBaseRenderer, MarkdownBlockStyles, MarkdownChannelMentionRenderer,
     MarkdownEmojiRenderer, MarkdownImageRenderer, MarkdownLatexRenderer, MarkdownTextStyles, SearchPattern, UserMentionKey, HighlightWithoutNotificationKey,
diff --git a/app/components/post_list/combined_user_activity/combined_user_activity.tsx b/app/components/post_list/combined_user_activity/combined_user_activity.tsx
index eafea6dd27b..c176b02905f 100644
--- a/app/components/post_list/combined_user_activity/combined_user_activity.tsx
+++ b/app/components/post_list/combined_user_activity/combined_user_activity.tsx
@@ -1,7 +1,7 @@
 // Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
 // See LICENSE.txt for license information.
 
-import React, {useCallback, useEffect} from 'react';
+import React, {useCallback, useEffect, useMemo} from 'react';
 import {useIntl} from 'react-intl';
 import {Keyboard, type StyleProp, TouchableHighlight, View, type ViewStyle} from 'react-native';
 
@@ -15,6 +15,7 @@ import {useIsTablet} from '@hooks/device';
 import {bottomSheetModalOptions, showModal, showModalOverCurrentContext} from '@screens/navigation';
 import {emptyFunction} from '@utils/general';
 import {getMarkdownTextStyles} from '@utils/markdown';
+import {isUserActivityProp} from '@utils/post_list';
 import {changeOpacity, makeStyleSheetFromTheme} from '@utils/theme';
 import {secureGetFromRecord} from '@utils/types';
 
@@ -71,6 +72,13 @@ const CombinedUserActivity = ({
     const content = [];
     const removedUserIds: string[] = [];
 
+    const userActivity = useMemo(() => {
+        if (isUserActivityProp(post?.props?.user_activity)) {
+            return post?.props?.user_activity;
+        }
+        return undefined;
+    }, [post?.props?.user_activity]);
+
     const getUsernames = (userIds: string[]) => {
         const someone = intl.formatMessage({id: 'channel_loader.someone', defaultMessage: 'Someone'});
         const you = intl.formatMessage({id: 'combined_system_message.you', defaultMessage: 'You'});
@@ -170,11 +178,12 @@ const CombinedUserActivity = ({
     };
 
     useEffect(() => {
-        if (!post) {
+        if (!userActivity) {
             return;
         }
 
-        const {allUserIds, allUsernames} = post.props.user_activity;
+        const allUserIds = userActivity.allUserIds;
+        const allUsernames = userActivity.allUsernames;
         if (allUserIds.length) {
             fetchMissingProfilesByIds(serverUrl, allUserIds);
         }
@@ -182,14 +191,14 @@ const CombinedUserActivity = ({
         if (allUsernames.length) {
             fetchMissingProfilesByUsernames(serverUrl, allUsernames);
         }
-    }, [post?.props.user_activity.allUserIds, post?.props.user_activity.allUsernames]);
+    }, [userActivity?.allUserIds, userActivity?.allUsernames]);
 
     if (!post) {
         return null;
     }
 
     const itemTestID = `${testID}.${post.id}`;
-    const {messageData} = post.props.user_activity;
+    const messageData = userActivity?.messageData || [];
     for (const message of messageData) {
         const {postType, actorId} = message;
         const userIds = new Set<string>(message.userIds);
diff --git a/app/components/post_list/combined_user_activity/index.ts b/app/components/post_list/combined_user_activity/index.ts
index 5ad70b51367..de0b5b6e703 100644
--- a/app/components/post_list/combined_user_activity/index.ts
+++ b/app/components/post_list/combined_user_activity/index.ts
@@ -11,7 +11,7 @@ import {queryPostsById} from '@queries/servers/post';
 import {observePermissionForPost} from '@queries/servers/role';
 import {observeCurrentUserId} from '@queries/servers/system';
 import {observeUser, queryUsersByIdsOrUsernames} from '@queries/servers/user';
-import {generateCombinedPost, getPostIdsForCombinedUserActivityPost} from '@utils/post_list';
+import {generateCombinedPost, getPostIdsForCombinedUserActivityPost, isUserActivityProp} from '@utils/post_list';
 
 import CombinedUserActivity from './combined_user_activity';
 
@@ -35,10 +35,11 @@ const withCombinedPosts = withObservables(['postId'], ({database, postId}: WithD
     const usernamesById = post.pipe(
         switchMap(
             (p) => {
-                if (!p) {
+                const userActivity = isUserActivityProp(p?.props?.user_activity) ? p.props.user_activity : undefined;
+                if (!userActivity) {
                     return of$<Record<string, string>>({});
                 }
-                return queryUsersByIdsOrUsernames(database, p.props.user_activity.allUserIds, p.props.user_activity.allUsernames).observeWithColumns(['username']).
+                return queryUsersByIdsOrUsernames(database, userActivity.allUserIds, userActivity.allUsernames).observeWithColumns(['username']).
                     pipe(
                         // eslint-disable-next-line max-nested-callbacks
                         switchMap((users) => {
diff --git a/app/components/post_list/post/avatar/avatar.tsx b/app/components/post_list/post/avatar/avatar.tsx
index 22e56729550..ac8f8aa4cbe 100644
--- a/app/components/post_list/post/avatar/avatar.tsx
+++ b/app/components/post_list/post/avatar/avatar.tsx
@@ -14,6 +14,7 @@ import {useServerUrl} from '@context/server';
 import {useTheme} from '@context/theme';
 import {openAsBottomSheet} from '@screens/navigation';
 import {preventDoubleTap} from '@utils/tap';
+import {ensureString} from '@utils/types';
 
 import type PostModel from '@typings/database/models/servers/post';
 import type UserModel from '@typings/database/models/servers/user';
@@ -39,12 +40,15 @@ const Avatar = ({author, enablePostIconOverride, isAutoReponse, location, post}:
 
     const fromWebHook = post.props?.from_webhook === 'true';
     const iconOverride = enablePostIconOverride && post.props?.use_user_icon !== 'true';
+    const propsIconUrl = ensureString(post.props?.override_icon_url);
+    const propsUsername = ensureString(post.props?.override_username);
+
     if (fromWebHook && iconOverride) {
         const isEmoji = Boolean(post.props?.override_icon_emoji);
         const frameSize = ViewConstant.PROFILE_PICTURE_SIZE;
         const pictureSize = isEmoji ? ViewConstant.PROFILE_PICTURE_EMOJI_SIZE : ViewConstant.PROFILE_PICTURE_SIZE;
         const borderRadius = isEmoji ? 0 : ViewConstant.PROFILE_PICTURE_SIZE / 2;
-        const overrideIconUrl = buildAbsoluteUrl(serverUrl, post.props?.override_icon_url);
+        const overrideIconUrl = buildAbsoluteUrl(serverUrl, propsIconUrl);
 
         let iconComponent: ReactNode;
         if (overrideIconUrl) {
@@ -95,8 +99,8 @@ const Avatar = ({author, enablePostIconOverride, isAutoReponse, location, post}:
             userId: author.id,
             channelId: post.channelId,
             location,
-            userIconOverride: post.props?.override_username,
-            usernameOverride: post.props?.override_icon_url,
+            userIconOverride: propsIconUrl,
+            usernameOverride: propsUsername,
         };
 
         Keyboard.dismiss();
diff --git a/app/components/post_list/post/body/add_members/add_members.tsx b/app/components/post_list/post/body/add_members/add_members.tsx
index 0217af3e830..c9a0247b287 100644
--- a/app/components/post_list/post/body/add_members/add_members.tsx
+++ b/app/components/post_list/post/body/add_members/add_members.tsx
@@ -14,6 +14,7 @@ import {useServerUrl} from '@context/server';
 import {t} from '@i18n';
 import {getMarkdownTextStyles} from '@utils/markdown';
 import {changeOpacity, makeStyleSheetFromTheme} from '@utils/theme';
+import {isStringArray} from '@utils/types';
 
 import type PostModel from '@typings/database/models/servers/post';
 import type UserModel from '@typings/database/models/servers/user';
@@ -26,6 +27,39 @@ type AddMembersProps = {
     theme: Theme;
 }
 
+export type AddMemberPostProps = {
+    post_id: string;
+    not_in_channel_user_ids?: string[];
+    not_in_groups_usernames?: string[];
+    not_in_channel_usernames?: string[];
+    user_ids?: string[];
+    usernames?: string[];
+}
+
+export function isAddMemberProps(v: unknown): v is AddMemberPostProps {
+    if (typeof v !== 'object' || !v) {
+        return false;
+    }
+
+    if (!('post_id' in v) || typeof v.post_id !== 'string') {
+        return false;
+    }
+
+    if (('not_in_channel_user_ids' in v) && !isStringArray(v.not_in_channel_user_ids)) {
+        return false;
+    }
+
+    if (('not_in_groups_usernames' in v) && !isStringArray(v.not_in_groups_usernames)) {
+        return false;
+    }
+
+    if (('not_in_channel_usernames' in v) && !isStringArray(v.not_in_channel_usernames)) {
+        return false;
+    }
+
+    return true;
+}
+
 const getStyleSheet = makeStyleSheetFromTheme((theme: Theme) => {
     return {
         message: {
@@ -41,20 +75,17 @@ const AddMembers = ({channelType, currentUser, location, post, theme}: AddMember
     const styles = getStyleSheet(theme);
     const textStyles = getMarkdownTextStyles(theme);
     const serverUrl = useServerUrl();
-    const postId: string = post.props.add_channel_member?.post_id;
-    const noGroupsUsernames = post.props.add_channel_member?.not_in_groups_usernames;
-    let userIds: string[] = post.props.add_channel_member?.not_in_channel_user_ids;
-    let usernames: string[] = post.props.add_channel_member?.not_in_channel_usernames;
-
-    if (!postId || !channelType) {
+    if (!isAddMemberProps(post.props?.add_channel_member)) {
         return null;
     }
 
-    if (!userIds) {
-        userIds = post.props.add_channel_member?.user_ids;
-    }
-    if (!usernames) {
-        usernames = post.props.add_channel_member?.usernames;
+    const postId = post.props.add_channel_member.post_id;
+    const noGroupsUsernames = post.props.add_channel_member.not_in_groups_usernames || [];
+    const userIds = post.props.add_channel_member.not_in_channel_user_ids || post.props.add_channel_member.user_ids || [];
+    const usernames = post.props.add_channel_member.not_in_channel_usernames || post.props.add_channel_member?.usernames || [];
+
+    if (!postId || !channelType) {
+        return null;
     }
 
     const handleAddChannelMember = () => {
diff --git a/app/components/post_list/post/body/content/embedded_bindings/button_binding/index.tsx b/app/components/post_list/post/body/content/embedded_bindings/button_binding/index.tsx
index b4b6fbc4d38..dafa0671e4d 100644
--- a/app/components/post_list/post/body/content/embedded_bindings/button_binding/index.tsx
+++ b/app/components/post_list/post/body/content/embedded_bindings/button_binding/index.tsx
@@ -15,7 +15,7 @@ import {observeChannel} from '@queries/servers/channel';
 import {observeCurrentTeamId} from '@queries/servers/system';
 import {showAppForm} from '@screens/navigation';
 import {createCallContext} from '@utils/apps';
-import {getStatusColors} from '@utils/message_attachment_colors';
+import {getStatusColors} from '@utils/message_attachment';
 import {preventDoubleTap} from '@utils/tap';
 import {makeStyleSheetFromTheme, changeOpacity} from '@utils/theme';
 
diff --git a/app/components/post_list/post/body/content/embedded_bindings/index.tsx b/app/components/post_list/post/body/content/embedded_bindings/index.tsx
index 3c6d1a3858c..afad7f7d2d2 100644
--- a/app/components/post_list/post/body/content/embedded_bindings/index.tsx
+++ b/app/components/post_list/post/body/content/embedded_bindings/index.tsx
@@ -4,6 +4,9 @@
 import React from 'react';
 import {View} from 'react-native';
 
+import {isAppBinding, validateBindings} from '@utils/apps';
+import {isArrayOf} from '@utils/types';
+
 import EmbeddedBinding from './embedded_binding';
 
 import type PostModel from '@typings/database/models/servers/post';
@@ -16,7 +19,7 @@ type Props = {
 
 const EmbeddedBindings = ({location, post, theme}: Props) => {
     const content: React.ReactNode[] = [];
-    const embeds: AppBinding[] = post.props.app_bindings;
+    const embeds: AppBinding[] = isArrayOf<AppBinding>(post.props?.app_bindings, isAppBinding) ? validateBindings(post.props.app_bindings) : [];
 
     embeds.forEach((embed, i) => {
         content.push(
diff --git a/app/components/post_list/post/body/content/index.tsx b/app/components/post_list/post/body/content/index.tsx
index 38ae3b79b18..abf34b557ab 100644
--- a/app/components/post_list/post/body/content/index.tsx
+++ b/app/components/post_list/post/body/content/index.tsx
@@ -3,6 +3,7 @@
 
 import React from 'react';
 
+import {isMessageAttachmentArray} from '@utils/message_attachment';
 import {isYoutubeLink} from '@utils/url';
 
 import EmbeddedBindings from './embedded_bindings';
@@ -31,7 +32,9 @@ const contentType: Record<string, string> = {
 
 const Content = ({isReplyPost, layoutWidth, location, post, theme}: ContentProps) => {
     let type: string | undefined = post.metadata?.embeds?.[0].type;
-    if (!type && post.props?.app_bindings?.length) {
+
+    const nAppBindings = Array.isArray(post.props?.app_bindings) ? post.props.app_bindings.length : 0;
+    if (!type && nAppBindings) {
         type = contentType.app_bindings;
     }
 
@@ -39,6 +42,8 @@ const Content = ({isReplyPost, layoutWidth, location, post, theme}: ContentProps
         return null;
     }
 
+    const attachments = isMessageAttachmentArray(post.props?.attachments) ? post.props.attachments : [];
+
     switch (contentType[type]) {
         case contentType.image:
             return (
@@ -74,10 +79,10 @@ const Content = ({isReplyPost, layoutWidth, location, post, theme}: ContentProps
                 />
             );
         case contentType.message_attachment:
-            if (post.props.attachments?.length) {
+            if (attachments.length) {
                 return (
                     <MessageAttachments
-                        attachments={post.props.attachments}
+                        attachments={attachments}
                         channelId={post.channelId}
                         layoutWidth={layoutWidth}
                         location={location}
@@ -89,7 +94,7 @@ const Content = ({isReplyPost, layoutWidth, location, post, theme}: ContentProps
             }
             break;
         case contentType.app_bindings:
-            if (post.props.app_bindings?.length) {
+            if (nAppBindings) {
                 return (
                     <EmbeddedBindings
                         location={location}
diff --git a/app/components/post_list/post/body/content/message_attachments/action_button/index.tsx b/app/components/post_list/post/body/content/message_attachments/action_button/index.tsx
index 328c85a5036..76f6c329284 100644
--- a/app/components/post_list/post/body/content/message_attachments/action_button/index.tsx
+++ b/app/components/post_list/post/body/content/message_attachments/action_button/index.tsx
@@ -6,7 +6,7 @@ import React, {useCallback, useRef} from 'react';
 
 import {postActionWithCookie} from '@actions/remote/integrations';
 import {useServerUrl} from '@context/server';
-import {getStatusColors} from '@utils/message_attachment_colors';
+import {getStatusColors} from '@utils/message_attachment';
 import {preventDoubleTap} from '@utils/tap';
 import {makeStyleSheetFromTheme, changeOpacity} from '@utils/theme';
 import {secureGetFromRecord} from '@utils/types';
diff --git a/app/components/post_list/post/body/content/message_attachments/message_attachment.tsx b/app/components/post_list/post/body/content/message_attachments/message_attachment.tsx
index 97f1afd271e..02d95c944a5 100644
--- a/app/components/post_list/post/body/content/message_attachments/message_attachment.tsx
+++ b/app/components/post_list/post/body/content/message_attachments/message_attachment.tsx
@@ -5,7 +5,7 @@ import React from 'react';
 import {View} from 'react-native';
 
 import {getMarkdownBlockStyles, getMarkdownTextStyles} from '@utils/markdown';
-import {getStatusColors} from '@utils/message_attachment_colors';
+import {getStatusColors} from '@utils/message_attachment';
 import {changeOpacity, makeStyleSheetFromTheme} from '@utils/theme';
 import {secureGetFromRecord} from '@utils/types';
 import {isValidUrl} from '@utils/url';
diff --git a/app/components/post_list/post/body/index.tsx b/app/components/post_list/post/body/index.tsx
index ea58760933d..7d14238f424 100644
--- a/app/components/post_list/post/body/index.tsx
+++ b/app/components/post_list/post/body/index.tsx
@@ -96,8 +96,11 @@ const Body = ({
     let body;
     let message;
 
+    const nBindings = Array.isArray(post.props?.app_bindings) ? post.props?.app_bindings.length : 0;
+    const nAttachments = Array.isArray(post.props?.attachments) ? post.props?.attachments.length : 0;
+
     const isReplyPost = Boolean(post.rootId && (!isEphemeral || !hasBeenDeleted) && location !== THREAD);
-    const hasContent = Boolean((post.metadata?.embeds?.length || (appsEnabled && post.props?.app_bindings?.length)) || post.props?.attachments?.length);
+    const hasContent = Boolean((post.metadata?.embeds?.length || (appsEnabled && nBindings)) || nAttachments);
 
     const replyBarStyle = useCallback((): StyleProp<ViewStyle>|undefined => {
         if (!isReplyPost || (isCRTEnabled && location === Screens.PERMALINK)) {
diff --git a/app/components/post_list/post/body/message/message.tsx b/app/components/post_list/post/body/message/message.tsx
index f15cfb2c1a9..d8101ce8d34 100644
--- a/app/components/post_list/post/body/message/message.tsx
+++ b/app/components/post_list/post/body/message/message.tsx
@@ -1,11 +1,12 @@
 // Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
 // See LICENSE.txt for license information.
 
-import React, {useCallback, useState} from 'react';
+import React, {useCallback, useMemo, useState} from 'react';
 import {type LayoutChangeEvent, ScrollView, useWindowDimensions, View} from 'react-native';
 import Animated from 'react-native-reanimated';
 
 import Markdown from '@components/markdown';
+import {isChannelMentions} from '@components/markdown/channel_mention/channel_mention';
 import {SEARCH} from '@constants/screens';
 import {useShowMoreAnimatedStyle} from '@hooks/show_more';
 import {getMarkdownTextStyles, getMarkdownBlockStyles} from '@utils/markdown';
@@ -69,6 +70,10 @@ const Message = ({currentUser, isHighlightWithoutNotificationLicensed, highlight
     const onLayout = useCallback((event: LayoutChangeEvent) => setHeight(event.nativeEvent.layout.height), []);
     const onPress = () => setOpen(!open);
 
+    const channelMentions = useMemo(() => {
+        return isChannelMentions(post.props?.channel_mentions) ? post.props.channel_mentions : {};
+    }, [post.props?.channel_mentions]);
+
     return (
         <>
             <Animated.View style={animatedStyle}>
@@ -86,7 +91,7 @@ const Message = ({currentUser, isHighlightWithoutNotificationLicensed, highlight
                             baseTextStyle={style.message}
                             blockStyles={blockStyles}
                             channelId={post.channelId}
-                            channelMentions={post.props?.channel_mentions}
+                            channelMentions={channelMentions}
                             imagesMetadata={post.metadata?.images}
                             isEdited={isEdited}
                             isReplyPost={isReplyPost}
@@ -100,7 +105,7 @@ const Message = ({currentUser, isHighlightWithoutNotificationLicensed, highlight
                             highlightKeys={isHighlightWithoutNotificationLicensed ? (currentUser?.highlightKeys ?? EMPTY_HIGHLIGHT_KEYS) : EMPTY_HIGHLIGHT_KEYS}
                             searchPatterns={searchPatterns}
                             theme={theme}
-                            isUnsafeLinksPost={post.props.unsafe_links && post.props.unsafe_links !== ''}
+                            isUnsafeLinksPost={Boolean(post.props?.unsafe_links && post.props.unsafe_links !== '')}
                         />
                     </View>
                 </ScrollView>
diff --git a/app/components/post_list/post/header/header.tsx b/app/components/post_list/post/header/header.tsx
index f79583e8dc9..76649cb34f6 100644
--- a/app/components/post_list/post/header/header.tsx
+++ b/app/components/post_list/post/header/header.tsx
@@ -12,6 +12,7 @@ import {useTheme} from '@context/theme';
 import {DEFAULT_LOCALE} from '@i18n';
 import {postUserDisplayName} from '@utils/post';
 import {makeStyleSheetFromTheme} from '@utils/theme';
+import {ensureString} from '@utils/types';
 import {typography} from '@utils/typography';
 import {displayUsername, getUserCustomStatus, getUserTimezone, isCustomStatusExpired} from '@utils/user';
 
@@ -96,6 +97,8 @@ const Header = (props: HeaderProps) => {
         isCustomStatusEnabled && displayName && customStatus &&
         !(isSystemPost || author?.isBot || isAutoResponse || isWebHook),
     ) && !isCustomStatusExpired(author) && Boolean(customStatus?.emoji);
+    const userIconOverride = ensureString(post.props?.override_icon_url);
+    const usernameOverride = ensureString(post.props?.override_username);
 
     return (
         <>
@@ -109,9 +112,9 @@ const Header = (props: HeaderProps) => {
                         rootPostAuthor={rootAuthorDisplayName}
                         shouldRenderReplyButton={shouldRenderReplyButton}
                         theme={theme}
-                        userIconOverride={post.props?.override_icon_url}
+                        userIconOverride={userIconOverride}
                         userId={post.userId}
-                        usernameOverride={post.props?.override_username}
+                        usernameOverride={usernameOverride}
                         showCustomStatusEmoji={showCustomStatusEmoji}
                         customStatus={customStatus!}
                     />
diff --git a/app/components/post_list/post/system_message/system_message.tsx b/app/components/post_list/post/system_message/system_message.tsx
index f7c88540452..9339b619793 100644
--- a/app/components/post_list/post/system_message/system_message.tsx
+++ b/app/components/post_list/post/system_message/system_message.tsx
@@ -12,7 +12,7 @@ import {useTheme} from '@context/theme';
 import {t} from '@i18n';
 import {getMarkdownTextStyles} from '@utils/markdown';
 import {changeOpacity, makeStyleSheetFromTheme} from '@utils/theme';
-import {secureGetFromRecord} from '@utils/types';
+import {secureGetFromRecord, ensureString} from '@utils/types';
 import {typography} from '@utils/typography';
 
 import type PostModel from '@typings/database/models/servers/post';
@@ -101,8 +101,8 @@ const renderHeaderChangeMessage = ({post, author, location, styles, intl, theme}
     }
 
     const username = renderUsername(author.username);
-    const oldHeader = post.props?.old_header;
-    const newHeader = post.props?.new_header;
+    const oldHeader = ensureString(post.props?.old_header);
+    const newHeader = ensureString(post.props?.new_header);
     let localeHolder;
 
     if (post.props?.new_header) {
@@ -144,12 +144,12 @@ const renderPurposeChangeMessage = ({post, author, location, styles, intl, theme
     }
 
     const username = renderUsername(author.username);
-    const oldPurpose = post.props?.old_purpose;
-    const newPurpose = post.props?.new_purpose;
+    const oldPurpose = ensureString(post.props?.old_purpose);
+    const newPurpose = ensureString(post.props?.new_purpose);
     let localeHolder;
 
-    if (post.props?.new_purpose) {
-        if (post.props?.old_purpose) {
+    if (newPurpose) {
+        if (oldPurpose) {
             localeHolder = {
                 id: t('mobile.system_message.update_channel_purpose_message.updated_from'),
                 defaultMessage: '{username} updated the channel purpose from: {oldPurpose} to: {newPurpose}',
@@ -166,7 +166,7 @@ const renderPurposeChangeMessage = ({post, author, location, styles, intl, theme
 
         values = {username, oldPurpose, newPurpose};
         return renderMessage({post, styles, intl, location, localeHolder, values, skipMarkdown: true, theme});
-    } else if (post.props?.old_purpose) {
+    } else if (oldPurpose) {
         localeHolder = {
             id: t('mobile.system_message.update_channel_purpose_message.removed'),
             defaultMessage: '{username} removed the channel purpose (was: {oldPurpose})',
@@ -180,8 +180,8 @@ const renderPurposeChangeMessage = ({post, author, location, styles, intl, theme
 };
 
 const renderDisplayNameChangeMessage = ({post, author, location, styles, intl, theme}: RenderersProps) => {
-    const oldDisplayName = post.props?.old_displayname;
-    const newDisplayName = post.props?.new_displayname;
+    const oldDisplayName = ensureString(post.props?.old_displayname);
+    const newDisplayName = ensureString(post.props?.new_displayname);
 
     if (!(author?.username)) {
         return null;
@@ -224,13 +224,13 @@ const renderUnarchivedMessage = ({post, author, location, styles, intl, theme}:
 };
 
 const renderAddGuestToChannelMessage = ({post, location, styles, intl, theme}: RenderersProps, hideGuestTags: boolean) => {
-    if (!post.props.username || !post.props.addedUsername) {
+    const username = renderUsername(ensureString(post.props?.username));
+    const addedUsername = renderUsername(ensureString(post.props?.addedUsername));
+
+    if (!username || !addedUsername) {
         return null;
     }
 
-    const username = renderUsername(post.props.username);
-    const addedUsername = renderUsername(post.props.addedUsername);
-
     const localeHolder = hideGuestTags ? postTypeMessages[Post.POST_TYPES.ADD_TO_CHANNEL].one : {
         id: t('api.channel.add_guest.added'),
         defaultMessage: '{addedUsername} added to the channel as a guest by {username}.',
@@ -241,11 +241,11 @@ const renderAddGuestToChannelMessage = ({post, location, styles, intl, theme}: R
 };
 
 const renderGuestJoinChannelMessage = ({post, styles, location, intl, theme}: RenderersProps, hideGuestTags: boolean) => {
-    if (!post.props.username) {
+    const username = renderUsername(ensureString(post.props?.username));
+    if (!username) {
         return null;
     }
 
-    const username = renderUsername(post.props.username);
     const localeHolder = hideGuestTags ? postTypeMessages[Post.POST_TYPES.JOIN_CHANNEL].one : {
         id: t('api.channel.guest_join_channel.post_and_forget'),
         defaultMessage: '{username} joined the channel as a guest.',
diff --git a/app/helpers/api/user.ts b/app/helpers/api/user.ts
index f0576f5841f..bccc6bf5ec9 100644
--- a/app/helpers/api/user.ts
+++ b/app/helpers/api/user.ts
@@ -3,6 +3,7 @@
 
 import {General} from '@constants';
 import {MENTIONS_REGEX} from '@constants/autocomplete';
+import {isMessageAttachmentArray} from '@utils/message_attachment';
 
 export const getNeededAtMentionedUsernames = (usernames: Set<string>, posts: Post[], excludeUsername?: string) => {
     const usernamesToLoad = new Set<string>();
@@ -36,8 +37,9 @@ export const getNeededAtMentionedUsernames = (usernames: Set<string>, posts: Pos
         // These correspond to the fields searched by getMentionsEnabledFields on the server
         findNeededUsernames(post.message);
 
-        if (post.props?.attachments) {
-            for (const attachment of post.props.attachments) {
+        const attachments = isMessageAttachmentArray(post.props?.attachments) ? post.props.attachments : undefined;
+        if (attachments) {
+            for (const attachment of attachments) {
                 findNeededUsernames(attachment.pretext);
                 findNeededUsernames(attachment.text);
             }
diff --git a/app/products/calls/components/calls_custom_message/index.ts b/app/products/calls/components/calls_custom_message/index.ts
index 559a8e98197..a5cd48febd5 100644
--- a/app/products/calls/components/calls_custom_message/index.ts
+++ b/app/products/calls/components/calls_custom_message/index.ts
@@ -30,7 +30,7 @@ const enhanced = withObservables(['post'], ({serverUrl, post, database}: OwnProp
     );
 
     // The call is not active, so return early with what we need to render the post.
-    if (post.props.end_at) {
+    if (post.props?.end_at) {
         return {
             currentUser,
             isMilitaryTime,
diff --git a/app/products/calls/utils.test.ts b/app/products/calls/utils.test.ts
index cf59dc1c364..c9465fa4639 100644
--- a/app/products/calls/utils.test.ts
+++ b/app/products/calls/utils.test.ts
@@ -194,12 +194,12 @@ describe('getCallPropsFromPost', () => {
 
         const props = getCallPropsFromPost(post);
 
-        expect(props.title).toBe(post.props.title);
-        expect(props.start_at).toBe(post.props.start_at);
-        expect(props.end_at).toBe(post.props.end_at);
-        expect(props.recordings).toBe(post.props.recordings);
-        expect(props.recording_files).toBe(post.props.recording_files);
-        expect(props.transcriptions).toBe(post.props.transcriptions);
-        expect(props.participants).toBe(post.props.participants);
+        expect(props.title).toBe(post.props?.title);
+        expect(props.start_at).toBe(post.props?.start_at);
+        expect(props.end_at).toBe(post.props?.end_at);
+        expect(props.recordings).toBe(post.props?.recordings);
+        expect(props.recording_files).toBe(post.props?.recording_files);
+        expect(props.transcriptions).toBe(post.props?.transcriptions);
+        expect(props.participants).toBe(post.props?.participants);
     });
 });
diff --git a/app/products/calls/utils.ts b/app/products/calls/utils.ts
index 13969feb07b..2b1917d1325 100644
--- a/app/products/calls/utils.ts
+++ b/app/products/calls/utils.ts
@@ -2,6 +2,7 @@
 // See LICENSE.txt for license information.
 
 import {makeCallsBaseAndBadgeRGB, rgbToCSS} from '@mattermost/calls';
+import {type CallsConfig, type CallPostProps, isCaption, type Caption, isCallJobMetadata, type CallJobMetadata} from '@mattermost/calls/lib/types';
 import {Alert} from 'react-native';
 import {SelectedTrackType, TextTrackType, type ISO639_1, type SelectedTrack, type TextTracks} from 'react-native-video';
 
@@ -9,6 +10,7 @@ import {buildFileUrl} from '@actions/remote/file';
 import {Calls, Post} from '@constants';
 import {NOTIFICATION_SUB_TYPE} from '@constants/push_notification';
 import {isMinimumServerVersion} from '@utils/helpers';
+import {ensureNumber, ensureString, isArrayOf, isRecordOf, isStringArray} from '@utils/types';
 import {displayUsername} from '@utils/user';
 
 import type {
@@ -17,7 +19,6 @@ import type {
     CallsTheme,
     CallsVersion,
 } from '@calls/types/calls';
-import type {CallsConfig, Caption, CallPostProps} from '@mattermost/calls/lib/types';
 import type PostModel from '@typings/database/models/servers/post';
 import type UserModel from '@typings/database/models/servers/user';
 import type {IntlShape} from 'react-intl';
@@ -217,17 +218,17 @@ export function isCallsStartedMessage(payload?: NotificationData) {
     return (payload?.message === 'You\'ve been invited to a call' || callsMessageRegex.test(payload?.message || ''));
 }
 
-export const hasCaptions = (postProps?: Record<string, any> & { captions?: Caption[] }): boolean => {
-    return !(!postProps || !postProps.captions?.[0]);
+export const hasCaptions = (postProps?: Record<string, unknown>): boolean => {
+    return Boolean(isArrayOf<Caption>(postProps?.captions, isCaption) && postProps.captions[0]);
 };
 
-export const getTranscriptionUri = (serverUrl: string, postProps?: Record<string, any> & { captions?: Caption[] }): {
+export const getTranscriptionUri = (serverUrl: string, postProps?: Record<string, unknown>): {
     tracks?: TextTracks;
     selected: SelectedTrack;
 } => {
     // Note: We're not using hasCaptions above because this tells typescript that the caption exists later.
     // We could use some fancy typescript to do the same, but it's not worth the complexity.
-    if (!postProps || !postProps.captions?.[0]) {
+    if (!isArrayOf<Caption>(postProps?.captions, isCaption) || !postProps.captions[0]) {
         return {
             tracks: undefined,
             selected: {type: SelectedTrackType.DISABLED, value: ''},
@@ -247,20 +248,16 @@ export const getTranscriptionUri = (serverUrl: string, postProps?: Record<string
     };
 };
 
-function isValidObject(v: any) {
-    return typeof v === 'object' && !Array.isArray(v) && v !== null;
-}
-
 export function getCallPropsFromPost(post: PostModel | Post): CallPostProps {
     return {
-        title: typeof post.props?.title === 'string' ? post.props.title : '',
-        start_at: typeof post.props?.start_at === 'number' ? post.props.start_at : 0,
-        end_at: typeof post.props?.end_at === 'number' ? post.props.end_at : 0,
-        recordings: isValidObject(post.props?.recordings) ? post.props.recordings : {},
-        transcriptions: isValidObject(post.props?.transcriptions) ? post.props.transcriptions : {},
-        participants: Array.isArray(post.props?.participants) ? post.props.participants : [],
+        title: ensureString(post.props?.title),
+        start_at: ensureNumber(post.props?.start_at),
+        end_at: ensureNumber(post.props?.end_at),
+        recordings: isRecordOf<CallJobMetadata>(post.props?.recordings, isCallJobMetadata) ? post.props.recordings : {},
+        transcriptions: isRecordOf<CallJobMetadata>(post.props?.transcriptions, isCallJobMetadata) ? post.props.transcriptions : {},
+        participants: isStringArray(post.props?.participants) ? post.props.participants : [],
 
         // DEPRECATED
-        recording_files: Array.isArray(post.props?.recording_files) ? post.props.recording_files : [],
+        recording_files: isStringArray(post.props?.recording_files) ? post.props.recording_files : [],
     };
 }
diff --git a/app/screens/gallery/footer/footer.tsx b/app/screens/gallery/footer/footer.tsx
index 9969468a8c7..a12b0e0c18f 100644
--- a/app/screens/gallery/footer/footer.tsx
+++ b/app/screens/gallery/footer/footer.tsx
@@ -9,6 +9,7 @@ import {SafeAreaView, type Edge, useSafeAreaInsets} from 'react-native-safe-area
 import {Events} from '@constants';
 import {GALLERY_FOOTER_HEIGHT} from '@constants/gallery';
 import {changeOpacity} from '@utils/theme';
+import {ensureString} from '@utils/types';
 import {displayUsername} from '@utils/user';
 
 import Actions from './actions';
@@ -71,14 +72,14 @@ const Footer = ({
 
     let overrideIconUrl;
     if (enablePostIconOverride && post?.props?.use_user_icon !== 'true' && post?.props?.override_icon_url) {
-        overrideIconUrl = post.props.override_icon_url;
+        overrideIconUrl = ensureString(post.props.override_icon_url);
     }
 
     let userDisplayName;
     if (item.type === 'avatar') {
         userDisplayName = item.name;
     } else if (enablePostUsernameOverride && post?.props?.override_username) {
-        userDisplayName = post.props.override_username as string;
+        userDisplayName = ensureString(post.props.override_username);
     } else {
         userDisplayName = displayUsername(author, undefined, teammateNameDisplay);
     }
diff --git a/app/utils/apps.ts b/app/utils/apps.ts
index bd21068c690..0f2fb2426db 100644
--- a/app/utils/apps.ts
+++ b/app/utils/apps.ts
@@ -4,6 +4,7 @@
 import {AppBindingLocations, AppCallResponseTypes, AppFieldTypes} from '@constants/apps';
 
 import {generateId} from './general';
+import {isArrayOf, isStringArray} from './types';
 
 export function cleanBinding(binding: AppBinding, topLocation: string): AppBinding|null {
     return cleanBindingRec(binding, topLocation, 0);
@@ -253,3 +254,297 @@ export const makeCallErrorResponse = (errMessage: string): AppCallResponse<any>
 };
 
 export const filterEmptyOptions = (option: AppSelectOption): boolean => Boolean(option.value && !option.value.match(/^[ \t]+$/));
+
+function isAppExpand(v: unknown): v is AppExpand {
+    if (typeof v !== 'object' || v === null) {
+        return false;
+    }
+
+    const expand = v as AppExpand;
+
+    if (expand.app !== undefined && typeof expand.app !== 'string') {
+        return false;
+    }
+
+    if (expand.acting_user !== undefined && typeof expand.acting_user !== 'string') {
+        return false;
+    }
+
+    if (expand.channel !== undefined && typeof expand.channel !== 'string') {
+        return false;
+    }
+
+    if (expand.config !== undefined && typeof expand.config !== 'string') {
+        return false;
+    }
+
+    if (expand.mentioned !== undefined && typeof expand.mentioned !== 'string') {
+        return false;
+    }
+
+    if (expand.parent_post !== undefined && typeof expand.parent_post !== 'string') {
+        return false;
+    }
+
+    if (expand.post !== undefined && typeof expand.post !== 'string') {
+        return false;
+    }
+
+    if (expand.root_post !== undefined && typeof expand.root_post !== 'string') {
+        return false;
+    }
+
+    if (expand.team !== undefined && typeof expand.team !== 'string') {
+        return false;
+    }
+
+    if (expand.user !== undefined && typeof expand.user !== 'string') {
+        return false;
+    }
+
+    return true;
+}
+
+function isAppCall(obj: unknown): obj is AppCall {
+    if (typeof obj !== 'object' || obj === null) {
+        return false;
+    }
+
+    const call = obj as AppCall;
+
+    if (typeof call.path !== 'string') {
+        return false;
+    }
+
+    if (call.expand !== undefined && !isAppExpand(call.expand)) {
+        return false;
+    }
+
+    // Here we're assuming that 'state' can be of any type, so no type check for 'state'
+
+    return true;
+}
+
+function isAppFormValue(v: unknown): v is AppFormValue {
+    if (typeof v === 'string') {
+        return true;
+    }
+
+    if (typeof v === 'boolean') {
+        return true;
+    }
+
+    if (v === null) {
+        return true;
+    }
+
+    return isAppSelectOption(v);
+}
+
+function isAppSelectOption(v: unknown): v is AppSelectOption {
+    if (typeof v !== 'object' || v === null) {
+        return false;
+    }
+
+    const option = v as AppSelectOption;
+
+    if (typeof option.label !== 'string' || typeof option.value !== 'string') {
+        return false;
+    }
+
+    if (option.icon_data !== undefined && typeof option.icon_data !== 'string') {
+        return false;
+    }
+
+    return true;
+}
+
+function isAppField(v: unknown): v is AppField {
+    if (typeof v !== 'object' || v === null) {
+        return false;
+    }
+
+    const field = v as AppField;
+
+    if (typeof field.name !== 'string' || typeof field.type !== 'string') {
+        return false;
+    }
+
+    if (field.is_required !== undefined && typeof field.is_required !== 'boolean') {
+        return false;
+    }
+
+    if (field.readonly !== undefined && typeof field.readonly !== 'boolean') {
+        return false;
+    }
+
+    if (field.value !== undefined && !isAppFormValue(field.value)) {
+        return false;
+    }
+
+    if (field.description !== undefined && typeof field.description !== 'string') {
+        return false;
+    }
+
+    if (field.label !== undefined && typeof field.label !== 'string') {
+        return false;
+    }
+
+    if (field.hint !== undefined && typeof field.hint !== 'string') {
+        return false;
+    }
+
+    if (field.position !== undefined && typeof field.position !== 'number') {
+        return false;
+    }
+
+    if (field.modal_label !== undefined && typeof field.modal_label !== 'string') {
+        return false;
+    }
+
+    if (field.refresh !== undefined && typeof field.refresh !== 'boolean') {
+        return false;
+    }
+
+    if (field.options !== undefined && !isArrayOf(field.options, isAppSelectOption)) {
+        return false;
+    }
+
+    if (field.multiselect !== undefined && typeof field.multiselect !== 'boolean') {
+        return false;
+    }
+
+    if (field.lookup !== undefined && !isAppCall(field.lookup)) {
+        return false;
+    }
+
+    if (field.subtype !== undefined && typeof field.subtype !== 'string') {
+        return false;
+    }
+
+    if (field.min_length !== undefined && typeof field.min_length !== 'number') {
+        return false;
+    }
+
+    if (field.max_length !== undefined && typeof field.max_length !== 'number') {
+        return false;
+    }
+
+    return true;
+}
+
+function isAppForm(v: unknown): v is AppForm {
+    if (typeof v !== 'object' || v === null) {
+        return false;
+    }
+
+    const form = v as AppForm;
+
+    if (form.title !== undefined && typeof form.title !== 'string') {
+        return false;
+    }
+
+    if (form.header !== undefined && typeof form.header !== 'string') {
+        return false;
+    }
+
+    if (form.footer !== undefined && typeof form.footer !== 'string') {
+        return false;
+    }
+
+    if (form.icon !== undefined && typeof form.icon !== 'string') {
+        return false;
+    }
+
+    if (form.submit_buttons !== undefined && typeof form.submit_buttons !== 'string') {
+        return false;
+    }
+
+    if (form.cancel_button !== undefined && typeof form.cancel_button !== 'boolean') {
+        return false;
+    }
+
+    if (form.submit_on_cancel !== undefined && typeof form.submit_on_cancel !== 'boolean') {
+        return false;
+    }
+
+    if (form.fields !== undefined && !isArrayOf(form.fields, isAppField)) {
+        return false;
+    }
+
+    if (form.source !== undefined && !isAppCall(form.source)) {
+        return false;
+    }
+
+    if (form.submit !== undefined && !isAppCall(form.submit)) {
+        return false;
+    }
+
+    if (form.depends_on !== undefined && !isStringArray(form.depends_on)) {
+        return false;
+    }
+
+    return true;
+}
+
+export function isAppBinding(obj: unknown): obj is AppBinding {
+    if (typeof obj !== 'object' || obj === null) {
+        return false;
+    }
+
+    const binding = obj as AppBinding;
+
+    if (typeof binding.app_id !== 'string' || typeof binding.label !== 'string') {
+        return false;
+    }
+
+    if (binding.location !== undefined && typeof binding.location !== 'string') {
+        return false;
+    }
+
+    if (binding.icon !== undefined && typeof binding.icon !== 'string') {
+        return false;
+    }
+
+    if (binding.hint !== undefined && typeof binding.hint !== 'string') {
+        return false;
+    }
+
+    if (binding.description !== undefined && typeof binding.description !== 'string') {
+        return false;
+    }
+
+    if (binding.role_id !== undefined && typeof binding.role_id !== 'string') {
+        return false;
+    }
+
+    if (binding.depends_on_team !== undefined && typeof binding.depends_on_team !== 'boolean') {
+        return false;
+    }
+
+    if (binding.depends_on_channel !== undefined && typeof binding.depends_on_channel !== 'boolean') {
+        return false;
+    }
+
+    if (binding.depends_on_user !== undefined && typeof binding.depends_on_user !== 'boolean') {
+        return false;
+    }
+
+    if (binding.depends_on_post !== undefined && typeof binding.depends_on_post !== 'boolean') {
+        return false;
+    }
+
+    if (binding.bindings !== undefined && !isArrayOf(binding.bindings, isAppBinding)) {
+        return false;
+    }
+
+    if (binding.form !== undefined && !isAppForm(binding.form)) {
+        return false;
+    }
+
+    if (binding.submit !== undefined && !isAppCall(binding.submit)) {
+        return false;
+    }
+
+    return true;
+}
diff --git a/app/utils/gallery/index.ts b/app/utils/gallery/index.ts
index 80148f71e9c..ba177001ceb 100644
--- a/app/utils/gallery/index.ts
+++ b/app/utils/gallery/index.ts
@@ -29,7 +29,7 @@ export const clampVelocity = (velocity: number, minVelocity: number, maxVelocity
     return Math.max(Math.min(velocity, -minVelocity), -maxVelocity);
 };
 
-export const fileToGalleryItem = (file: FileInfo, authorId?: string, postProps?: Record<string, any>, lastPictureUpdate = 0): GalleryItemType => {
+export const fileToGalleryItem = (file: FileInfo, authorId?: string, postProps?: Record<string, unknown>, lastPictureUpdate = 0): GalleryItemType => {
     let type: GalleryItemType['type'] = 'file';
     if (isVideo(file)) {
         type = 'video';
diff --git a/app/utils/message_attachment.ts b/app/utils/message_attachment.ts
new file mode 100644
index 00000000000..10ec5ff50c4
--- /dev/null
+++ b/app/utils/message_attachment.ts
@@ -0,0 +1,195 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+import {isArrayOf} from './types';
+
+export function getStatusColors(theme: Theme): Dictionary<string> {
+    return {
+        good: '#00c100',
+        warning: '#dede01',
+        danger: theme.errorTextColor,
+        default: theme.centerChannelColor,
+        primary: theme.buttonBg,
+        success: theme.onlineIndicator,
+    };
+}
+
+export function isMessageAttachmentArray(v: unknown): v is MessageAttachment[] {
+    return isArrayOf(v, isMessageAttachment);
+}
+
+function isPostActionOption(v: unknown): v is PostActionOption {
+    if (typeof v !== 'object' || !v) {
+        return false;
+    }
+
+    if ('text' in v && typeof v.text !== 'string') {
+        return false;
+    }
+
+    if ('value' in v && typeof v.value !== 'string') {
+        return false;
+    }
+
+    return true;
+}
+
+function isPostAction(v: unknown): v is PostAction {
+    if (typeof v !== 'object' || !v) {
+        return false;
+    }
+
+    if (!('id' in v)) {
+        return false;
+    }
+
+    if (typeof v.id !== 'string') {
+        return false;
+    }
+
+    if (!('name' in v)) {
+        return false;
+    }
+
+    if (typeof v.name !== 'string') {
+        return false;
+    }
+
+    if ('type' in v && typeof v.type !== 'string') {
+        return false;
+    }
+
+    if ('disabled' in v && typeof v.disabled !== 'boolean') {
+        return false;
+    }
+
+    if ('style' in v && typeof v.style !== 'string') {
+        return false;
+    }
+
+    if ('data_source' in v && typeof v.data_source !== 'string') {
+        return false;
+    }
+
+    if ('options' in v && !isArrayOf(v.options, isPostActionOption)) {
+        return false;
+    }
+
+    if ('default_option' in v && typeof v.default_option !== 'string') {
+        return false;
+    }
+
+    if ('cookie' in v && typeof v.cookie !== 'string') {
+        return false;
+    }
+
+    return true;
+}
+
+function isMessageAttachmentField(v: unknown) {
+    if (typeof v !== 'object') {
+        return false;
+    }
+
+    if (!v) {
+        return false;
+    }
+
+    if (!('title' in v)) {
+        return false;
+    }
+
+    if (typeof v.title !== 'string') {
+        return false;
+    }
+
+    if (!('value' in v)) {
+        return false;
+    }
+
+    if (typeof v.value === 'object' && v.value && 'toString' in v.value && typeof v.value.toString !== 'function') {
+        return false;
+    }
+
+    if ('short' in v && typeof v.short !== 'boolean') {
+        return false;
+    }
+
+    return true;
+}
+
+function isMessageAttachment(v: unknown): v is MessageAttachment {
+    if (typeof v !== 'object' || !v) {
+        return false;
+    }
+
+    if ('fallback' in v && typeof v.fallback !== 'string') {
+        return false;
+    }
+
+    // We may consider adding more validation to what color may be
+    if ('color' in v && typeof v.color !== 'string') {
+        return false;
+    }
+
+    if ('pretext' in v && typeof v.pretext !== 'string') {
+        return false;
+    }
+
+    if ('author_name' in v && typeof v.author_name !== 'string') {
+        return false;
+    }
+
+    // Where it is used, we are calling isUrlSafe. We could consider calling it here
+    if ('author_link' in v && typeof v.author_link !== 'string') {
+        return false;
+    }
+
+    // We may need more validation since this is going to be passed to an img src prop
+    if ('author_icon' in v && typeof v.author_icon !== 'string') {
+        return false;
+    }
+
+    if ('title' in v && typeof v.title !== 'string') {
+        return false;
+    }
+
+    // Where it is used, we are calling isUrlSafe. We could consider calling it here
+    if ('title_link' in v && typeof v.title_link !== 'string') {
+        return false;
+    }
+
+    if ('text' in v && typeof v.text !== 'string') {
+        return false;
+    }
+
+    // We may need more validation since this is going to be passed to an img src prop
+    if ('image_url' in v && typeof v.image_url !== 'string') {
+        return false;
+    }
+
+    // We may need more validation since this is going to be passed to an img src prop
+    if ('thumb_url' in v && typeof v.thumb_url !== 'string') {
+        return false;
+    }
+
+    // We are truncating if the size is more than some constant. We could check this here
+    if ('footer' in v && typeof v.footer !== 'string') {
+        return false;
+    }
+
+    // We may need more validation since this is going to be passed to an img src prop
+    if ('footer_icon' in v && typeof v.footer_icon !== 'string') {
+        return false;
+    }
+
+    if ('fields' in v && v.fields !== null && !isArrayOf(v.fields, isMessageAttachmentField)) {
+        return false;
+    }
+
+    if ('actions' in v && !isArrayOf(v.actions, isPostAction)) {
+        return false;
+    }
+
+    return true;
+}
diff --git a/app/utils/message_attachment_colors.test.ts b/app/utils/message_attachment_colors.test.ts
index 3ee07e98404..bea0b023342 100644
--- a/app/utils/message_attachment_colors.test.ts
+++ b/app/utils/message_attachment_colors.test.ts
@@ -3,7 +3,7 @@
 
 import {Preferences} from '@constants';
 
-import {getStatusColors} from './message_attachment_colors';
+import {getStatusColors} from './message_attachment';
 
 describe('getStatusColors', () => {
     const mockTheme = Preferences.THEMES.denim;
diff --git a/app/utils/message_attachment_colors.ts b/app/utils/message_attachment_colors.ts
deleted file mode 100644
index 210e02d0893..00000000000
--- a/app/utils/message_attachment_colors.ts
+++ /dev/null
@@ -1,13 +0,0 @@
-// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
-// See LICENSE.txt for license information.
-
-export function getStatusColors(theme: Theme): Dictionary<string> {
-    return {
-        good: '#00c100',
-        warning: '#dede01',
-        danger: theme.errorTextColor,
-        default: theme.centerChannelColor,
-        primary: theme.buttonBg,
-        success: theme.onlineIndicator,
-    };
-}
diff --git a/app/utils/post/index.test.ts b/app/utils/post/index.test.ts
index 463577f2bd4..b6620ea2b8f 100644
--- a/app/utils/post/index.test.ts
+++ b/app/utils/post/index.test.ts
@@ -85,7 +85,7 @@ describe('post utils', () => {
             const post = {
                 props: {
                     from_webhook: 'true',
-                },
+                } as Record<string, unknown>,
             } as PostModel;
 
             const result = isFromWebhook(post);
@@ -96,7 +96,7 @@ describe('post utils', () => {
             const post = {
                 props: {
                     from_webhook: 'false',
-                },
+                } as Record<string, unknown>,
             } as PostModel;
 
             const result = isFromWebhook(post);
@@ -149,7 +149,7 @@ describe('post utils', () => {
             const post = {
                 props: {
                     failed: true,
-                },
+                } as Record<string, unknown>,
                 pendingPostId: 'id',
                 id: 'id',
                 updateAt: Date.now() - Post.POST_TIME_TO_FAIL - 1000,
@@ -471,7 +471,7 @@ describe('post utils', () => {
                 props: {
                     from_webhook: 'true',
                     override_username: 'webhook_user',
-                },
+                } as Record<string, unknown>,
             } as PostModel;
 
             const result = postUserDisplayName(post, undefined, undefined, true);
@@ -482,7 +482,7 @@ describe('post utils', () => {
             const post = {
                 props: {
                     from_webhook: 'false',
-                },
+                } as Record<string, unknown>,
             } as PostModel;
             const author = {
                 username: 'user1',
@@ -497,7 +497,7 @@ describe('post utils', () => {
             const post = {
                 props: {
                     from_webhook: 'false',
-                },
+                } as Record<string, unknown>,
             } as PostModel;
             const author = {
                 username: 'user1',
diff --git a/app/utils/post/index.ts b/app/utils/post/index.ts
index 7cceeed5f08..dd29cdd5c6e 100644
--- a/app/utils/post/index.ts
+++ b/app/utils/post/index.ts
@@ -11,6 +11,7 @@ import DatabaseManager from '@database/manager';
 import {DEFAULT_LOCALE} from '@i18n';
 import {getUserById} from '@queries/servers/user';
 import {toMilliseconds} from '@utils/datetime';
+import {ensureString} from '@utils/types';
 import {displayUsername, getUserIdFromChannelName} from '@utils/user';
 
 import type PostModel from '@typings/database/models/servers/post';
@@ -36,7 +37,7 @@ export function areConsecutivePosts(post: PostModel, previousPost: PostModel) {
 }
 
 export function isFromWebhook(post: PostModel | Post): boolean {
-    return post.props && post.props.from_webhook === 'true';
+    return post.props?.from_webhook === 'true';
 }
 
 export function isEdited(post: PostModel): boolean {
@@ -48,7 +49,7 @@ export function isPostEphemeral(post: PostModel): boolean {
 }
 
 export function isPostFailed(post: PostModel): boolean {
-    return post.props?.failed || ((post.pendingPostId === post.id) && (Date.now() > post.updateAt + POST_TIME_TO_FAIL));
+    return Boolean(post.props?.failed) || ((post.pendingPostId === post.id) && (Date.now() > post.updateAt + POST_TIME_TO_FAIL));
 }
 
 export function isPostPendingOrFailed(post: PostModel): boolean {
@@ -64,8 +65,13 @@ export function fromAutoResponder(post: PostModel): boolean {
 }
 
 export function postUserDisplayName(post: PostModel, author?: UserModel, teammateNameDisplay?: string, enablePostUsernameOverride = false) {
-    if (isFromWebhook(post) && post.props?.override_username && enablePostUsernameOverride) {
-        return post.props.override_username;
+    const overrideUsername = ensureString(post.props?.override_username);
+    if (
+        isFromWebhook(post) &&
+        enablePostUsernameOverride &&
+        overrideUsername
+    ) {
+        return overrideUsername;
     }
 
     return displayUsername(author, author?.locale || DEFAULT_LOCALE, teammateNameDisplay, true);
diff --git a/app/utils/post_list/index.test.ts b/app/utils/post_list/index.test.ts
index 29432aafb81..64cff6488a1 100644
--- a/app/utils/post_list/index.test.ts
+++ b/app/utils/post_list/index.test.ts
@@ -319,7 +319,7 @@ describe('generateCombinedPost', () => {
         const result = generateCombinedPost('combined-post-id', systemPosts);
 
         // Ensure all post ids are included in the system_post_ids prop
-        expect(result.props.system_post_ids).toEqual(['post1', 'post2', 'post3']);
+        expect(result.props?.system_post_ids).toEqual(['post1', 'post2', 'post3']);
     });
 
     it('should include combined messages in the props object', () => {
@@ -331,7 +331,7 @@ describe('generateCombinedPost', () => {
         const result = generateCombinedPost('combined-post-id', systemPosts);
 
         // Ensure the messages prop includes all individual messages
-        expect(result.props.messages).toEqual(['Message 1', 'Message 2']);
+        expect(result.props?.messages).toEqual(['Message 1', 'Message 2']);
     });
 
     it('should set the post type to COMBINED_USER_ACTIVITY', () => {
@@ -387,7 +387,7 @@ describe('generateCombinedPost', () => {
         const result = generateCombinedPost(combinedPostId, systemPosts);
 
         // Extract the post types from the sorted messages in the combined post props
-        const sortedPostTypes = result.props.user_activity_posts.map((post: PostModel) => post.type);
+        const sortedPostTypes = (result.props?.user_activity_posts as any).map((post: PostModel) => post.type);
 
         // Expect the post types to be sorted based on their priorities in comparePostTypes
         expect(sortedPostTypes).toEqual([
@@ -422,9 +422,9 @@ describe('generateCombinedPost', () => {
         const result = generateCombinedPost(combinedPostId, systemPosts);
 
         // Ensure user activities are combined for ADD_TO_TEAM
-        expect(result.props.user_activity_posts.length).toBe(2);
-        expect(result.props.user_activity_posts[0].props.addedUserId).toBe('user1');
-        expect(result.props.user_activity_posts[1].props.addedUserId).toBe('user2');
+        expect((result.props?.user_activity_posts as any).length).toBe(2);
+        expect((result.props?.user_activity_posts as any)[0].props.addedUserId).toBe('user1');
+        expect((result.props?.user_activity_posts as any)[1].props.addedUserId).toBe('user2');
     });
 
     it('should combine user activity for REMOVE_FROM_CHANNEL posts correctly', () => {
@@ -451,9 +451,9 @@ describe('generateCombinedPost', () => {
         const result = generateCombinedPost(combinedPostId, systemPosts);
 
         // Ensure user activities are combined for REMOVE_FROM_CHANNEL
-        expect(result.props.user_activity_posts.length).toBe(2);
-        expect(result.props.user_activity_posts[0].props.removedUserId).toBe('user3');
-        expect(result.props.user_activity_posts[1].props.removedUserId).toBe('user4');
+        expect((result.props?.user_activity_posts as any).length).toBe(2);
+        expect((result.props?.user_activity_posts as any)[0].props.removedUserId).toBe('user3');
+        expect((result.props?.user_activity_posts as any)[1].props.removedUserId).toBe('user4');
     });
 
     it('should handle empty systemPosts gracefully', () => {
diff --git a/app/utils/post_list/index.ts b/app/utils/post_list/index.ts
index b5f7496659b..76f6e2a212f 100644
--- a/app/utils/post_list/index.ts
+++ b/app/utils/post_list/index.ts
@@ -6,6 +6,7 @@ import moment from 'moment-timezone';
 import {Post} from '@constants';
 import {toMilliseconds} from '@utils/datetime';
 import {isFromWebhook} from '@utils/post';
+import {ensureString, isArrayOf, isStringArray} from '@utils/types';
 
 import type {PostList, PostWithPrevAndNext} from '@typings/components/post_list';
 import type PostModel from '@typings/database/models/servers/post';
@@ -154,9 +155,11 @@ function isJoinLeavePostForUsername(post: PostModel, currentUsername: string): b
         return false;
     }
 
-    if (post.props.user_activity_posts) {
+    // We can be more lax with the types here because the recursive function only checks
+    // whether it is an array, or comparison with strings, so it should be safe enough.
+    if (Array.isArray(post.props.user_activity_posts)) {
         for (const childPost of post.props.user_activity_posts as PostModel[]) {
-            if (isJoinLeavePostForUsername(childPost, currentUsername)) {
+            if (childPost && isJoinLeavePostForUsername(childPost, currentUsername)) {
                 // If any of the contained posts are for this user, the client will
                 // need to figure out how to render the post
                 return true;
@@ -264,8 +267,8 @@ function combineUserActivitySystemPost(systemPosts: PostModel[]) {
             postType === Post.POST_TYPES.ADD_TO_CHANNEL ||
             postType === Post.POST_TYPES.REMOVE_FROM_CHANNEL
         ) {
-            const userId = post.props.addedUserId || post.props.removedUserId;
-            const username = post.props.addedUsername || post.props.removedUsername;
+            const userId = ensureString(post.props?.addedUserId) || ensureString(post.props?.removedUserId);
+            const username = ensureString(post.props?.addedUsername) || ensureString(post.props?.removedUsername);
             if (combinedPostType) {
                 if (Array.isArray(combinedPostType[post.userId])) {
                     throw new Error('Invalid Post activity data');
@@ -384,3 +387,55 @@ export function shouldFilterJoinLeavePost(post: PostModel, showJoinLeave: boolea
     // Don't filter out join/leave messages about the current user
     return !isJoinLeavePostForUsername(post, currentUsername);
 }
+
+export type MessageData = {
+    actorId: string;
+    postType: string;
+    userIds: string[];
+}
+
+function isMessageData(v: unknown): v is MessageData {
+    if (typeof v !== 'object' || !v) {
+        return false;
+    }
+
+    if (!('actorId' in v) || typeof v.actorId !== 'string') {
+        return false;
+    }
+
+    if (!('postType' in v) || typeof v.postType !== 'string') {
+        return false;
+    }
+
+    if (!('userIds' in v) || !isStringArray(v.userIds)) {
+        return false;
+    }
+
+    return true;
+}
+
+export type UserActivityProp = {
+    allUserIds: string[];
+    allUsernames: string[];
+    messageData: MessageData[];
+}
+
+export function isUserActivityProp(v: unknown): v is UserActivityProp {
+    if (typeof v !== 'object' || !v) {
+        return false;
+    }
+
+    if (!('allUserIds' in v) || !isStringArray(v.allUserIds)) {
+        return false;
+    }
+
+    if (!('allUsernames' in v) || !isStringArray(v.allUsernames)) {
+        return false;
+    }
+
+    if (!('messageData' in v) || !isArrayOf(v.messageData, isMessageData)) {
+        return false;
+    }
+
+    return true;
+}
diff --git a/app/utils/types.ts b/app/utils/types.ts
index 40c8ff17faa..a78a3b8bfc8 100644
--- a/app/utils/types.ts
+++ b/app/utils/types.ts
@@ -1,6 +1,42 @@
 // Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
 // See LICENSE.txt for license information.
 
+export function isArrayOf<T>(v: unknown, check: (e: unknown) => boolean): v is T[] {
+    if (!Array.isArray(v)) {
+        return false;
+    }
+
+    return v.every(check);
+}
+
+export function isStringArray(v: unknown): v is string[] {
+    return isArrayOf(v, (e) => typeof e === 'string');
+}
+
+export function isRecordOf<T>(v: unknown, check: (e: unknown) => boolean): v is Record<string, T> {
+    if (typeof v !== 'object' || !v) {
+        return false;
+    }
+
+    if (!(Object.keys(v).every((k) => typeof k === 'string'))) {
+        return false;
+    }
+
+    if (!(Object.values(v).every(check))) {
+        return false;
+    }
+
+    return true;
+}
+
+export function ensureString(v: unknown): string {
+    return typeof v === 'string' ? v : '';
+}
+
+export function ensureNumber(v: unknown): number {
+    return typeof v === 'number' ? v : 0;
+}
+
 export function secureGetFromRecord<T>(v: Record<string, T> | undefined, key: string) {
     return typeof v === 'object' && v && Object.prototype.hasOwnProperty.call(v, key) ? v[key] : undefined;
 }
diff --git a/package-lock.json b/package-lock.json
index d7a5d4ccd6c..616f26d4736 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -17,7 +17,7 @@
         "@formatjs/intl-numberformat": "8.10.3",
         "@formatjs/intl-pluralrules": "5.2.14",
         "@gorhom/bottom-sheet": "4.6.4",
-        "@mattermost/calls": "github:mattermost/calls-common#07607cf603f1e3f0c86ae248b2332e8da17f9cf8",
+        "@mattermost/calls": "github:mattermost/calls-common#030ff7c0a37ee9b0ccc5fae0b2ea9c0e1c08473f",
         "@mattermost/compass-icons": "0.1.45",
         "@mattermost/hardware-keyboard": "file:./libraries/@mattermost/hardware-keyboard",
         "@mattermost/keyboard-tracker": "file:./libraries/@mattermost/keyboard-tracker",
@@ -5837,11 +5837,11 @@
     "node_modules/@mattermost/calls": {
       "name": "@mattermost/calls-common",
       "version": "0.27.2",
-      "resolved": "git+ssh://git@github.com/mattermost/calls-common.git#07607cf603f1e3f0c86ae248b2332e8da17f9cf8",
-      "integrity": "sha512-aZIYwtgRVj8tdWJUPtAr4TPNa6tNM3lnRkC74CkSsFCpwZ1miwov0B4TLYG4Srj1rTgUqUwG3gQz4o5JHJ2fuQ==",
+      "resolved": "git+ssh://git@github.com/mattermost/calls-common.git#030ff7c0a37ee9b0ccc5fae0b2ea9c0e1c08473f",
+      "integrity": "sha512-qtMUUGHrl6VOGgjyQ+Ft4YddWo5RV8MDK8zSaYRU/1MiiY/zqq5kW6nvuzMB2S0xAvPwYlcFEBfmM4QZrReD6w==",
       "dependencies": {
-        "@msgpack/msgpack": "^3.0.0-beta2",
-        "fflate": "^0.8.2"
+        "@msgpack/msgpack": "3.0.0-beta2",
+        "fflate": "0.8.2"
       }
     },
     "node_modules/@mattermost/calls/node_modules/@msgpack/msgpack": {
diff --git a/package.json b/package.json
index bf9a592feae..4ecea74abe6 100644
--- a/package.json
+++ b/package.json
@@ -18,7 +18,7 @@
     "@formatjs/intl-numberformat": "8.10.3",
     "@formatjs/intl-pluralrules": "5.2.14",
     "@gorhom/bottom-sheet": "4.6.4",
-    "@mattermost/calls": "github:mattermost/calls-common#07607cf603f1e3f0c86ae248b2332e8da17f9cf8",
+    "@mattermost/calls": "github:mattermost/calls-common#030ff7c0a37ee9b0ccc5fae0b2ea9c0e1c08473f",
     "@mattermost/compass-icons": "0.1.45",
     "@mattermost/hardware-keyboard": "file:./libraries/@mattermost/hardware-keyboard",
     "@mattermost/keyboard-tracker": "file:./libraries/@mattermost/keyboard-tracker",
diff --git a/types/api/files.d.ts b/types/api/files.d.ts
index 3e5f4d48bc6..0d0affb6fad 100644
--- a/types/api/files.d.ts
+++ b/types/api/files.d.ts
@@ -22,7 +22,7 @@ type FileInfo = {
     uri?: string;
     user_id: string;
     width: number;
-    postProps?: Record<string, any>;
+    postProps?: Record<string, unknown>;
 };
 
 type FilesState = {
diff --git a/types/api/posts.d.ts b/types/api/posts.d.ts
index a9b3a3c6031..01d350e0648 100644
--- a/types/api/posts.d.ts
+++ b/types/api/posts.d.ts
@@ -71,7 +71,7 @@ type Post = {
     message_source?: string;
     type: PostType;
     participants?: null | UserProfile[]|string[];
-    props: Record<string, any>;
+    props: Record<string, unknown> | undefined;
     hashtags: string;
     pending_post_id: string;
     reply_count: number;
diff --git a/types/database/models/servers/post.ts b/types/database/models/servers/post.ts
index e81b543bd04..e3a9be36a88 100644
--- a/types/database/models/servers/post.ts
+++ b/types/database/models/servers/post.ts
@@ -71,7 +71,7 @@ declare class PostModel extends Model {
     userId: string;
 
     /** props : Additional attributes for this props */
-    props: any;
+    props: Record<string, unknown> | null;
 
     /** drafts  : Every draft associated with this Post */
     drafts: Query<DraftModel>;
diff --git a/types/screens/gallery.ts b/types/screens/gallery.ts
index 44cec0860d9..950586b0590 100644
--- a/types/screens/gallery.ts
+++ b/types/screens/gallery.ts
@@ -76,7 +76,7 @@ export type GalleryItemType = {
     authorId?: string;
     size?: number;
     postId?: string;
-    postProps?: Record<string, any> & {captions?: Caption[]};
+    postProps?: Record<string, unknown> & {captions?: Caption[]};
 };
 
 export type GalleryAction = 'none' | 'downloading' | 'copying' | 'sharing' | 'opening' | 'external';