CWE-53: Path Equivalence: '\multiple\\internal\backslash'

What is Path Equivalence: '\multiple\\internal\backslash'?

• Overview: Path Equivalence with multiple internal backslashes is a vulnerability where the software accepts input paths containing sequences like '\multiple\internal\backslash' without proper validation. This can result in ambiguous path resolution, allowing attackers to traverse the file system and access or modify unintended files.

• Exploitation Methods:

• Attackers can exploit this vulnerability by crafting input paths with multiple backslashes to bypass access controls or gain unauthorized access to files.
• Common attack patterns include directory traversal and bypassing security checks designed to prevent access to sensitive directories.

• Security Impact:

• Direct consequences of successful exploitation include unauthorized file access, data manipulation, and potential execution of arbitrary code.
• Potential cascading effects might involve further system compromise, data breaches, or exposure of sensitive information.
• Business impact could include loss of customer trust, legal liabilities, and financial losses due to data breaches or service disruptions.

• Prevention Guidelines:

• Specific code-level fixes include normalizing paths by resolving redundant separators and ensuring consistent path representations before any security checks.
• Security best practices involve implementing strict input validation and sanitization to prevent malicious path input.
• Recommended tools and frameworks include using libraries that provide robust path handling APIs, such as pathlib in Python or java.nio.file in Java, to avoid manual path manipulation errors.

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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 user input without validation
    # Multiple backslashes can lead to unintended path resolution
    with open(file_path, 'r') as file:  # Opens file directly without path validation
        return file.read()

# Example of vulnerable usage
user_input_path = input("Enter the file path: ")
print(read_file(user_input_path))  # User input is used directly, leading to potential path traversal

How to fix Path Equivalence: '\multiple\internal\backslash'?

To fix the vulnerability related to path equivalence due to multiple backslashes, it's essential to normalize the path to ensure all logical paths are resolved consistently. This can be achieved by using os.path.normpath() in Python, which removes redundant separators and up-level references.

Additionally, it's crucial to validate the resolved path against a whitelist of allowed directories or use a secure method to check if the path leads to a legitimate and expected location. This ensures that the application does not inadvertently access or manipulate unintended files.

Fixed Code Example

import os

def read_file(file_path):
    # Normalize the path to prevent path equivalence issues
    normalized_path = os.path.normpath(file_path)  # Normalize path to avoid path traversal
    
    # Validate the normalized path
    if not os.path.isfile(normalized_path):
        raise ValueError("Invalid file path")  # Ensure the path points to a file
    
    # Ensure the path is within an expected directory (e.g., '/safe/directory/')
    allowed_directory = os.path.abspath('/safe/directory/')
    if not os.path.commonpath([allowed_directory, normalized_path]).startswith(allowed_directory):
        raise ValueError("Access to this path is not allowed")  # Prevent access outside the allowed directory

    with open(normalized_path, 'r') as file:
        return file.read()

# Example of secure usage
user_input_path = input("Enter the file path: ")
try:
    print(read_file(user_input_path))
except ValueError as e:
    print(f"Error: {e}")

In the fixed code, os.path.normpath() is applied to the user input to normalize the path, removing redundant separators and resolving any relative paths. The code checks if the normalized path is a file and then ensures that the file path is within a specific allowed directory using os.path.commonpath() to prevent unauthorized file access. This approach mitigates the risk of path traversal and ensures that the file operations are performed securely.