1. Introduction
Directory Traversal — also known as Path Traversal — is a classic yet devastating vulnerability that allows attackers to access files and directories outside the intended scope of a web application. By manipulating file path inputs, an attacker can jump out of the application’s working directory and read, modify, or exfiltrate sensitive files.
Why it’s still critical in 2025:
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Legacy systems and insecure coding patterns still exist in production.
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APIs, IoT devices, and microservices often have inadequate path sanitization.
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Directory traversal remains a top entry point for data breaches, configuration leaks, and credential theft.
2. How Directory Traversal Works
When an application constructs file paths using user-supplied input without proper validation or sanitization, attackers can insert special path sequences to navigate up the directory tree.
Example payload:
Attack Flow:
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Vulnerable Endpoint – File download/view feature uses direct file path concatenation.
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Input Manipulation – Attacker injects
../sequences to move to parent directories. -
Target Access – Sensitive system files or application source code become accessible.
3. Common Targets in Directory Traversal Attacks
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Unix/Linux:
/etc/passwd,/etc/shadow -
Windows:
C:\Windows\System32\config\SAM -
Application Configs:
.env,config.php,database.yml -
Source Code:
.git/,/WEB-INF/web.xml -
Cloud Metadata (via local services):
/var/lib/cloud/instance/
4. Types of Directory Traversal
4.1 Relative Path Traversal
Using ../ sequences to navigate up the directory tree.
4.2 Absolute Path Traversal
Using a full path (e.g., /etc/passwd) if the application allows absolute references.
4.3 Encoded Path Traversal
Encoding traversal sequences to bypass filters:
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%2e%2e%2f→../ -
%252e%252e%252f(double encoding)
4.4 Null Byte Injection
On older systems, %00 can terminate a string early, bypassing file extension checks.
5. Real-World Incidents
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Fortinet VPN (2023) – Directory traversal allowed reading arbitrary system files, aiding RCE.
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GoAhead Web Server Exploit – Popular in IoT devices, traversal flaws exposed sensitive configs.
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GitLab 2022 – Path traversal in file upload feature exposed private repository data.
6. MITRE ATT&CK Mapping
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T1005 – Data from Local System
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T1083 – File and Directory Discovery
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T1552.001 – Credentials in Files
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T1213 – Data from Information Repositories
7. Advanced Exploitation Techniques in 2025
| Technique | Description | Example |
|---|---|---|
| Filter Bypass via Encoding | Obfuscating traversal strings to evade WAFs. | %252e%252e%252f |
| Parameter Pollution | Adding traversal sequences in unexpected parameters. | lang=../../../../etc/passwd |
| File Upload + Traversal | Combining malicious uploads with traversal to overwrite sensitive files. | Uploading shell to /var/www/html/../../tmp/ |
| Symlink Abuse | Pointing a symlink to sensitive files and accessing them via the app. | /uploads/symlink_to_shadow |
8. Detection & Prevention Strategies
A. Input Validation & Sanitization
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Reject
../,..\, or encoded equivalents in file paths. -
Use whitelisting for allowed file names.
B. Path Normalization
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Resolve and canonicalize paths before accessing files.
C. Least Privilege
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The application process should not have read/write access to sensitive OS files.
D. Virtual Chroot/Jailing
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Use chroot environments or containerized file access to isolate application directories.
E. Logging & Monitoring
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Detect traversal patterns in server logs.
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Use WAF rules to block common traversal payloads.
9. Threat Hunting Tips
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Look for
../patterns in HTTP request parameters and URLs. -
Review access logs for file requests outside the application directory.
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Monitor for repeated 403/404 errors targeting unusual file paths.
10. CyberDudeBivash Recommendations
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Red Team: Actively test file handling features with traversal payloads during pentests.
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Blue Team: Deploy anomaly detection for suspicious file access patterns.
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DevSecOps: Integrate path traversal checks into CI/CD pipelines.
Conclusion
Directory Traversal is deceptively simple but devastatingly effective. A single insecure file-handling function can expose entire systems. In modern DevSecOps workflows, preventing it is about rigorous input validation, isolation, and proactive testing.
Bottom line: Don’t let attackers take a stroll through your filesystem.
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