Directory traversal, also known as path traversal, is a web application vulnerability that allows an attacker to access files and directories outside the intended scope of the application. It occurs when a web application does not properly validate or sanitize user-supplied input used to construct file paths.
Here is a brief explanation of directory traversal and some techniques used:
- What is Directory Traversal?
Directory traversal occurs when an attacker manipulates input to traverse directories and access files that should be restricted. The goal is to bypass security mechanisms and retrieve sensitive information or execute arbitrary code.
- Techniques Used in Directory Traversal Attacks:
- Dot-dot-slash (../): This technique involves using “../” to navigate up the directory tree and access files in higher-level directories.
- URL encoding (%2e%2e/): Attackers may try to URL-encode the dot-dot-slash sequence to bypass input validation or filters.
- Null byte (%00): By appending a null byte to the end of a file name, attackers can truncate the name and access files with unintended extensions or locations.
- Alternate encoding and representation: Attackers may use different encoding schemes or character representations to obfuscate the traversal attempt and bypass filters.
- Example Scenarios:
Let’s consider a web application that serves files based on user-supplied input, such as a file download feature. If the application does not validate the input properly, an attacker could manipulate it to traverse directories and access restricted files, such as sensitive configuration files or user data. For example, suppose the application expects a parameter called “filename” to download a file. A legitimate request might look like:
An attacker could exploit directory traversal by manipulating the input as follows:
In this case, the attacker uses “../” to navigate to the parent directories until reaching the “/etc/passwd” file, which contains sensitive system information.
- Mitigation Techniques:
- Input Validation: Validate and sanitize user input to ensure it contains only the necessary characters and does not contain any path traversal sequences.
- Whitelisting: Maintain a whitelist of permitted files or directories and only allow access to those explicitly listed.
- File System Permissions: Set appropriate file system permissions to restrict access to sensitive files and directories.
- Web Application Firewalls (WAF): Implement a WAF that can detect and block directory traversal attempts.
It is crucial to be aware of and mitigate directory traversal vulnerabilities to prevent unauthorized access to sensitive files and data. Web application developers should follow secure coding practices and conduct regular security assessments to identify and address such vulnerabilities.
Remember, the purpose of this information is to understand and mitigate security vulnerabilities, not to engage in malicious activities.