CWE-48: Path Equivalence: 'file name' (Internal Whitespace)

What is Path Equivalence: 'file name' (Internal Whitespace)?

• Overview: Path Equivalence: 'file name' (Internal Whitespace) is a security vulnerability where a software product mistakenly accepts file paths with internal whitespace without proper validation. This can lead to ambiguous path resolutions, allowing attackers to traverse the filesystem and potentially access sensitive files or directories.

• Exploitation Methods:

• Attackers can exploit this vulnerability by crafting file paths that include spaces, causing the system to misinterpret or incorrectly resolve these paths.
• Common attack techniques involve directory traversal or file inclusion attacks, where attackers use specially crafted paths to access unauthorized files.

• Security Impact:

• Direct consequences include unauthorized access to sensitive files, data leakage, or execution of unintended files.
• Potential cascading effects may involve further system compromise if sensitive configuration files or credentials are accessed.
• Business impact could range from data breaches, violation of compliance standards, to reputational damage and financial loss.

• Prevention Guidelines:

• Implement strict input validation and normalization of file paths to remove or correctly handle spaces.
• Use security best practices such as whitelisting valid file paths and rejecting any ambiguous input.
• Recommended tools and frameworks include static code analysis tools that can detect path traversal vulnerabilities and libraries that safely handle file paths.

Corgea can automatically detect and fix Path Equivalence: 'file name' (Internal Whitespace) in your codebase. [Try Corgea free today](https://corgea.app).

Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Not Language-Specific

Affected Technologies: Not specified

Vulnerable Code Example

import os

def read_file(filename):
    """
    This function attempts to read a file from the filesystem.
    Vulnerable to path equivalence attacks due to internal whitespace.
    """
    # An attacker can exploit internal whitespace to access unintended files
    with open(filename, 'r') as file:
        return file.read()

user_input = "file name.txt"  # Example user input with internal whitespace
print(read_file(user_input))

Explanation

The vulnerable code above does not properly handle internal whitespace in file paths. This can lead to path equivalence issues where an attacker might manipulate file paths to access files that should not be accessible. The code directly uses the user-provided filename without any normalization or validation, making it susceptible to attacks.

How to fix Path Equivalence: 'file name' (Internal Whitespace)?

Path equivalence vulnerabilities arise when an application accepts file paths containing internal whitespace, which attackers can exploit to access files that should be restricted. The fix involves normalizing the path and validating it against a list of allowed paths or directories. This ensures that input paths cannot be manipulated to access unintended files.

1. Normalization: Use functions like os.path.normpath to resolve the input path to its simplest form, removing any redundant components like . or ...
2. Validation: Ensure that the normalized path is within a permitted directory. This prevents attackers from using path traversal techniques to escape designated directories.
3. User Input Sanitization: Strip whitespace and other potentially harmful characters from user input to prevent manipulation.

Fixed Code Example

import os

def read_file(filename):
    """
    This function reads a file from a designated directory, ensuring safe path resolution.
    It normalizes and validates the path to prevent path equivalence attacks.
    """
    # Normalize the input path to handle internal whitespace and path traversal
    safe_filename = os.path.normpath(filename.strip())

    # Define a secure base directory
    base_directory = '/secure_directory/'

    # Construct the full path
    full_path = os.path.join(base_directory, safe_filename)

    # Verify that the full_path is within the base directory
    if not os.path.commonpath([os.path.abspath(full_path), os.path.abspath(base_directory)]) == os.path.abspath(base_directory):
        raise ValueError("Access to this path is not allowed.")

    # Read the file safely if validation passes
    with open(full_path, 'r') as file:
        return file.read()

user_input = "file name.txt"
print(read_file(user_input))

Explanation

In the fixed example, the code normalizes the user-provided filename using os.path.normpath and strip() to remove unnecessary whitespace and resolve any path traversal attempts. The code then constructs the full path using os.path.join and checks if the resolved path is within a designated secure directory using os.path.commonpath. This prevents unauthorized access to files outside the intended directory, ensuring the security of file access operations.