CWE-354: Improper Validation of Integrity Check Value

What is Improper Validation of Integrity Check Value?

• Overview: Improper Validation of Integrity Check Value (CWE-354) occurs when a software product fails to correctly validate the integrity check values or checksums of a message. This can prevent the system from detecting if data has been altered or corrupted during transmission, leading to potential security risks.

• Exploitation Methods:

• Attackers can intercept and modify data in transit and then manipulate or spoof the integrity check value to match the altered data, bypassing detection.
• Common attack patterns include man-in-the-middle attacks where the attacker alters data and provides a false checksum to the receiving party.

• Security Impact:

• Direct consequences include the potential for data tampering without detection, leading to unauthorized access or manipulation of sensitive information.
• Potential cascading effects involve undermining trust in data integrity across interconnected systems, potentially leading to larger security breaches.
• Business impact involves loss of data integrity, customer trust, and potential legal and compliance issues due to failure to protect data adequately.

• Prevention Guidelines:

• Specific code-level fixes include implementing and rigorously verifying checksum algorithms as per protocol specifications to ensure data integrity.
• Security best practices involve using cryptographic hash functions for checksums and ensuring both ends of a communication channel validate checksums accurately.
• Recommended tools and frameworks include using libraries and tools that provide secure hashing functions, such as those compliant with standards like SHA-256, and employing secure transport protocols like TLS to protect data in transit.

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Technical Details

Likelihood of Exploit: Medium

Affected Languages: Not Language-Specific

Affected Technologies: Not specified

Vulnerable Code Example

import hashlib

def receive_file(file_content, received_checksum):
    # Calculate the checksum of the received file content
    calculated_checksum = hashlib.md5(file_content.encode()).hexdigest()
    
    # Vulnerable: Incorrectly trusting the received checksum without proper validation
    # If the received checksum is empty or malformed, it could bypass the integrity check
    if calculated_checksum == received_checksum:
        print("File received successfully and integrity verified.")
    else:
        print("File integrity check failed.")

Explanation of Vulnerability

In the vulnerable code example, the integrity check relies on an MD5 checksum, which is a weak hashing algorithm susceptible to collision attacks. Additionally, there is no validation of the format or length of the received checksum, allowing malformed or empty checksums to potentially bypass the integrity check.

How to fix Improper Validation of Integrity Check Value?

To fix the Improper Validation of Integrity Check Value vulnerability, ensure that the integrity check is robust and cannot be bypassed by malformed or absent checksums. Follow these best practices:

1. Validate the Format of the Checksum: Ensure that the received checksum has a valid format and length before comparing it.
2. Use a Stronger Hashing Algorithm: Consider using a more secure hashing algorithm like SHA-256 instead of MD5, which is considered weak.
3. Implement Error Handling: Add error handling to deal with unexpected or malformed data.
4. Use a Cryptographic Library for HMAC: Utilize HMAC (Hash-based Message Authentication Code) to ensure the integrity and authenticity of the data.

Fixed Code Example

import hashlib
import hmac

def receive_file(file_content, received_checksum, secret_key):
    # Calculate the HMAC of the received file content using a secret key
    calculated_hmac = hmac.new(secret_key.encode(), file_content.encode(), hashlib.sha256).hexdigest()
    
    # Fix: Validate the format of the received checksum and compare it securely using HMAC
    if isinstance(received_checksum, str) and len(received_checksum) == 64:  # SHA-256 produces a 64-character hex string
        if hmac.compare_digest(calculated_hmac, received_checksum):
            print("File received successfully and integrity verified.")
        else:
            print("File integrity check failed.")
    else:
        print("Invalid checksum format received.")

Explanation of Fix

In the fixed code example, several critical improvements were made:

• Stronger Hashing Algorithm: We replaced MD5 with SHA-256, a more secure hashing algorithm.
• HMAC Implementation: We used HMAC to ensure both the integrity and authenticity of the received data, which provides additional security by requiring a secret key.
• Checksum Format Validation: We added a check to ensure the received checksum is a string and matches the expected length of a SHA-256 hash, preventing malformed checksums from bypassing the integrity check.
• Secure Comparison: We used hmac.compare_digest() for a secure comparison that mitigates timing attacks, ensuring the integrity check cannot be bypassed through subtle timing differences.