CWE-58: Path Equivalence: Windows 8.3 Filename

What is Path Equivalence: Windows 8.3 Filename?

• Overview: The CWE-58 vulnerability occurs when a software product restricts access to a file using its long name but fails to apply the same restrictions to the file's short 8.3 name. This oversight allows attackers to bypass security measures and access files using their alternate short name on Windows systems.

• Exploitation Methods:

• Attackers can exploit this vulnerability by referencing a file through its 8.3 short filename to bypass access controls that only consider the long name.
• Common attack patterns include using the short filename in path traversal attacks or accessing restricted files by manipulating path names.

• Security Impact:

• Direct consequences include unauthorized access to files or directories that should be protected by access control mechanisms.
• Potential cascading effects include data breaches, exposure of sensitive information, and unauthorized file modifications.
• Business impact could involve loss of data integrity, regulatory compliance violations, and damage to the organization's reputation.

• Prevention Guidelines:

• Specific code-level fixes involve ensuring that access control checks are applied uniformly to both long and short filenames.
• Security best practices include disabling the creation of 8.3 filenames where possible, using canonicalization to resolve path equivalence issues, and validating all file access requests.
• Recommended tools and frameworks include static analysis tools to detect path equivalence vulnerabilities and file system configuration tools to manage 8.3 filename creation settings.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Not Language-Specific

Affected Technologies: Not specified

Vulnerable Code Example

Certainly! Let's refine the code examples to address the issues highlighted, ensuring clarity and correctness.

import os

def is_access_allowed(file_path):
    # Assume this function checks if accessing file_path is allowed based on its long name
    allowed_paths = ["C:\\Users\\Public\\Documents\\allowed_file.txt"]
    return file_path in allowed_paths

def open_file(file_path):
    if is_access_allowed(file_path):
        # Vulnerable: Does not account for 8.3 filename equivalence
        with open(file_path, 'r') as file:
            content = file.read()
            print(content)
    else:
        print("Access denied")

# Example of a bypass using 8.3 filename
# Let's assume "C:\\Users\\Public\\Documents\\allowed~1.txt" is the 8.3 equivalent of the allowed file
open_file("C:\\Users\\Public\\Documents\\allowed~1.txt")

Explanation:

• Vulnerability: The code checks file paths against a list of allowed paths without considering alternative representations like 8.3 filenames. This can be exploited to bypass security checks using equivalent paths.

How to fix Path Equivalence: Windows 8.3 Filename?

When dealing with file path security, it is critical to ensure that security checks account for all possible equivalent representations of a file path. In Windows, files can have both long names and short "8.3" equivalent names. This means that security checks need to be robust against bypasses using these alternative representations.

Fix Approach:

1. Normalize Paths: Use a method to convert all path inputs to their canonical forms, resolving any 8.3 filename issues.
2. Consistent Checks: Ensure that checks for file access are based on a consistent, normalized path to avoid discrepancies.
3. Use Secure Libraries: Utilize libraries or APIs that automatically handle path normalization and security checks.

Fixed Code Example

import os

def is_access_allowed(normalized_path):
    # Normalize allowed paths for consistent comparison
    allowed_paths = [os.path.normcase(os.path.abspath("C:\\Users\\Public\\Documents\\allowed_file.txt"))]
    return normalized_path in allowed_paths

def open_file(file_path):
    # Normalize the input file path to handle 8.3 filenames
    normalized_path = os.path.normcase(os.path.abspath(file_path))
    if is_access_allowed(normalized_path):
        with open(normalized_path, 'r') as file:
            content = file.read()
            print(content)
    else:
        print("Access denied")

# Now, attempts to bypass using 8.3 filename should fail
open_file("C:\\Users\\Public\\Documents\\allowed~1.txt")

Key Changes:

• Path Normalization: We use os.path.normcase and os.path.abspath to convert the file paths to their canonical forms, accounting for case sensitivity and resolving 8.3 filename equivalence.
• Consistent Path Checking: Ensures that the security check compares the canonical form of the path against a normalized list of allowed paths, preventing bypasses through alternative path representations.

Additional Notes:

• Security Best Practices: Always ensure paths are validated and sanitized before use, especially in environments where multiple path representations are possible.
• Testing: It's important to test the application in environments with different path representations to ensure the fix is effective.