CWE-47: Path Equivalence: ' filename' (Leading Space)

What is Path Equivalence: ' filename' (Leading Space)?

• Overview: This vulnerability occurs when a software application accepts file path inputs with leading spaces without proper validation. This can result in ambiguous path resolution, allowing attackers to access unintended files or directories by manipulating file paths.

• Exploitation Methods:

• Attackers can exploit this vulnerability by inserting leading spaces into file paths to bypass security checks or access control mechanisms.
• Common attack patterns include directory traversal attacks where attackers navigate to sensitive directories by leveraging the leading space to alter the perceived path.

• Security Impact:

• Direct consequences include unauthorized file access, allowing attackers to read, modify, or delete sensitive files.
• Potential cascading effects include gaining further access to the system, escalating privileges, or compromising the entire application.
• Business impact could be significant, including data breaches, loss of customer trust, legal liabilities, and financial damage.

• Prevention Guidelines:

• Specific code-level fixes include trimming leading and trailing whitespace from all path inputs before processing.
• Security best practices involve implementing strict input validation and sanitization for all file path entries.
• Recommended tools and frameworks include using built-in path normalization functions and libraries that handle path resolution securely, such as those provided by the operating system or secure coding libraries.

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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 to path equivalence with leading spaces
    # An attacker can use ' filename.txt' to access unintended files
    if os.path.exists(file_path):
        with open(file_path, 'r') as file:
            return file.read()
    else:
        return "File does not exist."

# Example usage
content = read_file(' user.txt')
print(content)

How to fix Path Equivalence: ' filename' (Leading Space)?

The primary issue with the vulnerable code is that it does not trim input paths to remove leading or trailing spaces. This can lead to ambiguous path resolution, allowing attackers to manipulate file access by using unintended paths. To fix this vulnerability, you should normalize the path by trimming any whitespace from user input before using it. This ensures that the path is correctly interpreted and checked against the intended path.

Additionally, it's advisable to perform further sanitization and validation, such as checking for path traversal characters, to enhance security further.

Fixed Code Example

import os

def read_file(file_path):
    # Normalize the path by stripping leading and trailing whitespace
    normalized_path = file_path.strip()

    # Check for path traversal characters
    if '..' in normalized_path or normalized_path.startswith('/'):
        return "Invalid file path."

    # Securely check and read the file
    if os.path.exists(normalized_path):
        with open(normalized_path, 'r') as file:
            return file.read()
    else:
        return "File does not exist."

# Example usage
content = read_file(' user.txt')
print(content)

In the fixed code, the key changes include:

• Line 6: Stripping leading and trailing whitespace from the file path using strip().
• Line 9: Adding a check for path traversal characters (..) and ensuring the path doesn't start with /, which are common indicators of malicious path manipulation.
• These changes ensure that the input path is both normalized and validated, preventing attackers from exploiting path equivalence vulnerabilities.