CWE-1386: Insecure Operation on Windows Junction / Mount Point

What is Insecure Operation on Windows Junction / Mount Point?

• Overview: This vulnerability occurs when a software application interacts with files or directories without properly ensuring that they are not linked to Windows junctions or mount points that redirect operations to unauthorized locations. Such redirection can lead to unintended file operations outside the application's intended control.

• Exploitation Methods:

• Attackers can exploit this vulnerability by creating junctions or mount points that redirect file operations to sensitive or unauthorized files.
• Common attack patterns include creating hard links to critical or sensitive files, allowing attackers to manipulate or access these files through privileged operations.

• Security Impact:

• Direct consequences of successful exploitation include unauthorized reading, writing, or deletion of files.
• Potential cascading effects include privilege escalation, where attackers gain higher-level access than intended.
• Business impact could involve data breaches, loss of data integrity, and potential legal repercussions from mishandling sensitive information.

• Prevention Guidelines:

• Specific code-level fixes include validating paths to ensure they do not resolve to junctions or mount points before performing file operations.
• Security best practices involve restricting file operations to trusted directories and using APIs that handle path resolution securely.
• Recommended tools and frameworks include using Windows-specific APIs that provide robust path validation, and incorporating static analysis tools to detect junction or mount point 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: Attempts to read a file without checking if the path is a junction or mount point
    # This can lead to unauthorized access if the path is manipulated using junctions
    with open(file_path, 'r') as file:
        data = file.read()
    return data

# Example usage
print(read_file('C:\\some\\path\\to\\file.txt'))

Explanation:

• Vulnerability: The read_file function opens a file directly from the provided path without checking if it's a junction or a symbolic link. An attacker could exploit this by creating a junction to a sensitive file, thereby gaining unauthorized access to its contents.

How to fix Insecure Operation on Windows Junction / Mount Point?

To fix this vulnerability, you should:

1. Check for Junctions: Before accessing a file, ensure the path does not resolve to a junction or symbolic link that points outside the intended directory.
2. Use Safe Libraries: Utilize libraries that provide functionality to safely resolve paths and check their integrity.
3. Restrict Access: Implement strict access control policies to ensure only authorized junctions and paths are accessed.

Fixed Code Example

import os

def read_file_safe(file_path):
    # Check if the path is a symbolic link or junction
    if os.path.islink(file_path) or os.path.ismount(file_path):
        raise ValueError("Access denied: The path is a symbolic link or junction.")
    
    # Resolve the absolute path
    absolute_path = os.path.realpath(file_path)
    
    # Verify that the resolved path begins with the intended directory
    intended_directory = os.path.abspath('C:\\some\\path\\')  # Define the base directory
    if not absolute_path.startswith(intended_directory):
        raise ValueError("Access denied: The path is outside the intended directory.")
    
    # Securely read the file
    with open(absolute_path, 'r') as file:
        data = file.read()
    return data

# Example usage
try:
    print(read_file_safe('C:\\some\\path\\to\\file.txt'))
except ValueError as e:
    print(e)

Explanation:

• Check for Junctions: The code now checks if the path is a symbolic link or mount point using os.path.islink and os.path.ismount, preventing unauthorized redirection.
• Resolve Paths Safely: It uses os.path.realpath to resolve the absolute path, ensuring it points within the intended control sphere.
• Directory Restriction: It verifies that the resolved path starts with the intended directory path, preventing unauthorized access to files outside the designated area.
• Error Handling: It raises exceptions if any checks fail, providing meaningful error messages and preventing unauthorized access.