CWE-38: Path Traversal: '\absolute\pathname\here'

What is Path Traversal: '\absolute\pathname\here'?

• Overview: Path Traversal through backslash absolute paths is a vulnerability where a software application improperly processes user input containing absolute paths with backslashes, allowing attackers to navigate the file system and access files outside the intended directories.

• Exploitation Methods:

• Attackers can exploit this vulnerability by crafting input that includes backslash absolute paths to navigate to sensitive files.
• Common attack patterns include injecting paths like '........\sensitive\file.txt' to move up directories and access restricted files.

• Security Impact:

• Direct consequences of successful exploitation include unauthorized access to sensitive files and data.
• Potential cascading effects involve further system compromise if critical files such as configuration files or authentication credentials are accessed.
• Business impact can be significant, including data breaches, loss of customer trust, and potential legal consequences.

• Prevention Guidelines:

• Specific code-level fixes include validating and sanitizing all user inputs to ensure they do not contain absolute paths or unexpected directory traversal sequences.
• Security best practices include implementing strict input validation, using whitelisting methods, and employing path normalization functions to handle file paths securely.
• Recommended tools and frameworks include static code analysis tools to detect path traversal vulnerabilities and web application firewalls (WAFs) to monitor and block malicious input patterns.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Not Language-Specific

Affected Technologies: Not specified

Vulnerable Code Example

import os

def read_file(file_path):
    # Vulnerable to path traversal attacks as it accepts input without validation
    with open(file_path, 'r') as file:
        return file.read()

# Example usage
file_content = read_file(r'\absolute\path\to\file.txt')
print(file_content)

In this vulnerable code example, the read_file function takes a file path as input and opens it directly. If this function is exposed to user input, an attacker can provide a path like \..\..\..\etc\passwd to read unauthorized files, leading to a path traversal vulnerability. This occurs because the function does not validate or sanitize the input file path, allowing traversal outside the intended directory.

How to fix Path Traversal: '\absolute\pathname\here'?

To fix this vulnerability, it's important to validate and sanitize the input file paths. One approach is to only allow access to files within a specific directory. This can be done by resolving the absolute path of the file and ensuring it starts with the expected base directory. Avoid accepting or constructing paths using untrusted user input without proper checks.

Fixed Code Example

import os

def read_file(file_path):
    base_directory = r'C:\safe\directory'  # Define a safe base directory
    # Resolve the absolute path and validate against the base directory
    absolute_path = os.path.abspath(os.path.join(base_directory, file_path))
    
    # Ensure that the resolved path is within the base directory
    if not absolute_path.startswith(os.path.abspath(base_directory) + os.sep):
        raise ValueError("Invalid file path!")  # Prevent path traversal
    
    with open(absolute_path, 'r') as file:
        return file.read()

# Example usage
try:
    file_content = read_file('file.txt')  # Safe usage within the defined base directory
    print(file_content)
except ValueError as e:
    print(e)

In the fixed code example, the function read_file now resolves the absolute path of the given file_path relative to a secure base directory. It checks if the resolved path starts with the base directory path. Note the use of os.sep to ensure the base directory path ends with a separator, preventing directory prefix attacks. If the check fails, it raises a ValueError, preventing unauthorized file access. This approach mitigates path traversal attacks by restricting file access to a known safe directory.