CWE-52: Path Equivalence: '/multiple/trailing/slash//'

What is Path Equivalence: '/multiple/trailing/slash//'?

• Overview: Path Equivalence vulnerability (CWE-52) occurs when a software system accepts file or directory paths with multiple trailing slashes without proper validation, potentially leading to incorrect or ambiguous path resolution. This can allow attackers to access unauthorized parts of the file system.

• Exploitation Methods:

• Attackers can manipulate user input to include multiple trailing slashes, tricking the software into resolving paths incorrectly.
• Common attack patterns include file path traversal, where additional slashes are used to bypass path validation checks or access restricted directories or files.

• Security Impact:

• Direct consequences include unauthorized file access, information disclosure, and potential compromise of sensitive files.
• Potential cascading effects include further system exploitation if attackers gain access to critical configuration files or scripts.
• Business impact can involve data breaches, legal consequences, and damage to brand reputation.

• Prevention Guidelines:

• Specific code-level fixes include normalizing paths by removing redundant slashes and validating paths against a whitelist of allowed directories.
• Security best practices involve implementing strict input validation and output encoding to prevent path manipulation.
• Recommended tools and frameworks include using libraries that safely handle file path operations and conducting regular security audits to identify and address path-related vulnerabilities.

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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 code: Accepts file path with potential for path equivalence issues
    if os.path.exists(file_path):
        with open(file_path, 'r') as file:
            return file.read()
    return None

Explanation:

In this code, the read_file function takes a file path as input and attempts to read the file's content. However, it does not handle path equivalence issues, such as multiple trailing slashes or symbolic links, which can lead to ambiguous path resolution. This vulnerability could allow an attacker to access unintended files if they manipulate the file path to bypass security checks.

How to fix Path Equivalence: '/multiple/trailing/slash//'?

To address this issue, normalize the file paths to ensure consistent resolution. In Python, os.path.normpath() can normalize the path by removing redundant separators and resolving symbolic links, ensuring the path is canonical. It's also good practice to validate the file path against a whitelist of allowed directories to prevent directory traversal attacks.

Fixed Code Example

import os

def read_file(file_path):
    # Normalize the file path to prevent path equivalence issues
    normalized_path = os.path.normpath(file_path)
    
    # Define a safe base directory
    base_dir = os.path.abspath("/safe/directory")
    
    # Ensure the normalized path is within the allowed base directory
    if os.path.commonpath([os.path.abspath(normalized_path), base_dir]) == base_dir:
        if os.path.exists(normalized_path):
            with open(normalized_path, 'r') as file:
                return file.read()
    return None

Key Fixes:

1. Normalization: Use os.path.normpath() to normalize the file path, removing redundant slashes and resolving symbolic links. {3}
2. Base Directory Check: Define a base directory and ensure that the normalized path resides within this directory using os.path.commonpath(). This prevents directory traversal attacks. {5-7}
3. Absolute Path Comparison: Convert both paths to absolute paths before comparison to ensure accuracy in path checking. {6}
4. Ensure Path Exists: Verify the existence of the normalized path before attempting to open the file. {8}

By applying these fixes, we ensure that the file paths are resolved correctly and securely, mitigating the risk of path equivalence vulnerabilities.