netscaler-content.sh

# Copyright 2023 Google LLC
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#   https://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

# FreeBSD/NetScaler bash doesn't support array declaration shortcut
# so we create the array by hand... I'm sorry.
declare -a ns_content_denylist;
# look for strings found in most of the eval shells
ns_content_denylist[0]="http_response_code([0-9]\{3\})";
ns_content_denylist[1]="str_rot13(";
ns_content_denylist[2]="base64_decode(\$_POST";
ns_content_denylist[3]="@\\\$_POST".
ns_content_denylist[4]="eval(\$_POST";
ns_content_denylist[4]="eval(\$_GET";
ns_content_denylist[5]="Expires: Wed, 11 Jan 1984 05:00:00";
ns_content_denylist[6]="@eval(";


# REGEORG.NEO tunneler
ns_content_denylist[7]="blv_encode";
ns_content_denylist[8]="sayhello";

# SECRETSAUCE webshell
ns_content_denylist[9]="get('openssl_public_decrypt')";

# misc bad seen in webshells
ns_content_denylist[10]="#nssecret#";
ns_content_denylist[11]="uRemote";

# bishopfox https://github.com/BishopFox/CVE-2023-3519/
ns_content_denylist[12]="<?=\`curl";

# mass scanning
ns_content_denylist[13]="168\.100\.11\.89:8000";

# port scanner
ns_content_denylist[14]="github\.com/lcvvv/kscan";

# tunnelers
# look for printable strings left from the build process
declare -a ns_binary_content_denylist;
ns_binary_content_denylist[0]="ligolo-ng";
ns_binary_content_denylist[1]="sshd/server\.go";
ns_binary_content_denylist[2]="test/httpdemo/main\.go";
ns_binary_content_denylist[3]="ehang\.io/nps";
ns_binary_content_denylist[4]="\[library-to-inject\]";
ns_binary_content_denylist[5]="UPX executable";

report_ns_matches() {
    entries="$1";
    for entry in $entries; do
        report_encoded_file_name "$entry";
    done
}

# Search the files in the given path for denylisted terms.
# The denylist is found above, at `ns_content_denylist`.
scan_ns_directory_content() {
    local readonly path="$root_directory";

    if [ ! -d "$path" ]; then
        debug "didn't find directory: $path";
        return
    fi

    local found=false;
    for re in "${ns_content_denylist[@]}"; do
        local findcmd="find -EL $path -type f";
        local entries=$($findcmd \( -not -path "/proc/*" -and -not -regex "/tmp/[0-9]{10}/.*" -and -not -regex "/var(/crash)?/nsproflog/newproflog.*" -and -not -regex "/var(/crash)?/log/notice.log" \) -exec grep -lI --null -e "$re" {} + | perl -0ne 'chomp; print(unpack("H*", $_), "\n")');
        if [ -n "$entries" ]; then
            found=true;
            report_match "denylisted content '$re'";
            report "matches for '$re':";
            report_ns_matches "$entries";
        fi
    done

    if [ "$found" != true ]; then
        debug "did not find denylisted or suspicious content in $path";
    fi
}

# scan binary files under 10mb for denylisted items. We do this separately so that we can
# look for webshells without scanning binary files unnecessarily
# The binary deny list is above at `ns_binary_content_denylist`
scan_ns_directory_binary_content() {
    local readonly path="$root_directory";

    if [ ! -d "$path" ]; then
        debug "didn't find directory: $path";
        return
    fi

    local found=false;
    for re in "${ns_binary_content_denylist[@]}"; do
        local findcmd="find -EL $path -type f -size -10M";
        local entries=$($findcmd \( -not -path "/proc/*" -and -not -regex "/tmp/[0-9]{10}/.*" -and -not -regex "/var(/crash)?/nsproflog/newproflog.*" -and -not -regex "/var(/crash)?/log/notice.log" \) -exec grep -l --null -e "$re" {} + | perl -0ne 'chomp; print(unpack("H*", $_), "\n")');
        if [ -n "$entries" ]; then
            found=true;
            report_match "denylisted content '$re' in binary file";
            report "matches for '$re':";
            report_ns_matches "$entries";
        fi
    done

    if [ "$found" != true ]; then
        debug "did not find denylisted or suspicious binary content in $path";
    fi
}

# Search the files in the given path for nobody:root ownership
# This is relatively rare and a good indication of post-exploitation
# files being dropped
scan_ns_file_ownership() {
    local readonly path="$root_directory";

    if [ ! -d "$path" ]; then
        debug "didn't find directory: $path";
        return
    fi

    local entries=$(find -L "$path" -type f -user nobody -gid 0 -not -path "/proc/*" -exec file {} \; | egrep -i "script|html|executable|compressed|archive" | awk -F":" '{print $1}' | perl -0ne 'chomp; print(unpack("H*", $_), "\n")');
    if [ -n "$entries" ]; then
        report_permission_match "suspicious file ownership";
        report "files with ownership nobody:root:";
        report_ns_matches "$entries";
        report "Please review the above paths for suspicious content.";
        report "Exploits commonly write to files with these permissions;"
    else
        debug "did not find incorrect permissions in $path";
    fi
}



scan_netscaler_content() {
        scan_ns_directory_content;
        scan_ns_directory_binary_content;
        scan_ns_file_ownership;
}