Path Traversal Vulnerability: How a Few Dots Can Open the Door to Your Business Data
- shaun9968
- May 12
- 4 min read
Introduction
Perhaps your business has a locked cabinet for your sensitive files. You keep it locked as you only want certain, authorised people to access the contents.
Now, picture someone slipping a note of paper into the gap in a cabinet drawer, with a sliver of a camera attached, that can then move about inside the cabinet and transmit pictures of documents.
This is the essence of a path traversal vulnerability - a subtle but powerful flaw in web applications that, if not secured, can allow attackers to bypass the file system and peek into files that are supposed to be fully protected.
What Is Path Traversal?
Path traversal, also known as directory traversal, is a type of vulnerability that allows a user to access files and directories without using the operating system folder and file structure used by a web application. This is done by exploiting how an application handles paths to file addresses (either on memory or on disk storage), especially when those paths are based on user input.
Most web applications allow users to download reports, access documents, or fetch images on a server via URLs or form inputs to name but a few. If these file requests are not properly validated or sanitized, attackers can manipulate the file path to "traverse" the server’s directory tree and reach the addresses of files they shouldn't be able to see.
How Path Traversal Works
It exploits what comes after the ? in a URL string. The core of the attack revolves around attacking the server using sequences like ../ (in Unix-based systems) or ..\ (in Windows) to move up one level in the directory tree.
Here’s a simple illustration:
Normal file access:
The application might interpret this as an instruction to access a server file structure like this:
/var/www/html/files/invoice.pdf
Malicious file access (Unix/Linux systems):
This can resolve to:
/etc/passwd, a sensitive file that lists user accounts on Unix systems.
If the application doesn’t validate the URL command properly, and does not impose restrictions on ?file= characters, it might serve this very private system file directly to the attacker.
What Can Attackers Access?
With a successful path traversal exploit, attackers may gain unauthorized access to:
· System configuration files (/etc/passwd, .env, web.config)
· Source code and internal application logic
· Authentication credentials and API keys
· Logs and audit trails
· Backup files, staging versions, or old code repositories
· Files containing customer data or even employee data
The list is not exhaustive but… if sensitive data is held on the server and not adequately protected, it might be up for grabs.
Why does Path Traversal Vulnerabilities Happen?
· Lack of input validation: Applications blindly trust user input and concatenate it into file paths.
· Poor sandboxing (separation of data): Applications allow access to file paths beyond a designated folder.
· Misconfigured servers: Server-side protections such as directory whitelisting or access restrictions are missing or weak.
· Legacy or custom code: Older code or in-house tools often lack modern security practices.
How Path Traversal Vulnerability could affect Businesses
· Data Breaches: Sensitive internal files, customer records, and credentials can be leaked, putting customers and operations at risk.
· Reputation Damage: News of a data breach spreads fast, customers lose trust, and competitors gain an edge. Many companies can find this extremely hard to recover from.
· Compliance Penalties: If personal data is exposed, companies may face steep fines under GDPR, or PCI-DSS regulations.
· Intellectual Property Theft: Source code or business plans may be accessed and misused by competitors or cybercriminals. Once its out there, anyone can use it to their advantage.
· Platform Takeover: Some files may reveal database credentials, internal APIs (Application programming interfaces) , or admin backdoors, leading to a full system compromise. If this happens, the business could face a real struggle to regain access.
Preventing Path Traversal: What Developers and Businesses Can Do
· Sanitize Input: never allow raw user input to dictate file paths. Use strict whitelists or validate input against known safe patterns (e.g., only allowing filenames from a database).
· Use only secure APIs
· Instead of manipulating paths manually, use secure methods to build code for file paths. For example, in the language Python, os.path.abspath() can help normalize paths and prevent traversal.
· Efficiently restrict File Access
· Ensure applications operate in a "sandboxed" directory and cannot access files outside it, using server controls like chroot or jailed environments.
· Use the principle of Least Privilege for user accounts
· Run your web services using limited permission accounts so that even if a traversal occurs, the attacker’s access is limited.
· Deploy a Web Application Firewall (WAF). Many antivirus products provide such a facility. This can help detect and block common traversal patterns in HTTP requests.
· Test! Try to hack your web page input boxes. Log and Monitor activity
· Enable logging of file access attempts and monitor for suspicious patterns such as repeated use of ../ in URLs.
· Conduct routine vulnerability scans and code reviews. Use tools like OWASP ZAP, Burp Suite, or commercial scanners to catch issues before attackers do.
Conclusion
Path traversal may seem like a technical detail, but the consequences of circumventing the official file system can be far-reaching - simple manipulation of file paths can give attackers access to your most sensitive business data.
Fortunately, this vulnerability that can be easily avoided with careful coding, validation, and regular security practices.
In cybersecurity, small oversights often open the biggest doors. Always validate input data and don’t let a few extra dots (../) in an input box be the reason your data is compromised!
Further Reading
What is path traversal article by OWASP:
Real life data breach example of Directory traversal article by Invicti:
A beginner’s guide to testing for path traversal attacks:
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