CWE-1290: Incorrect Decoding of Security Identifiers

What is Incorrect Decoding of Security Identifiers ?

• Overview: Incorrect Decoding of Security Identifiers (CWE-1290) occurs when a product's mechanism for decoding security identifiers from bus-transaction signals is flawed, allowing unauthorized entities to gain access to protected assets.

• Exploitation Methods:

• Attackers can exploit this vulnerability by manipulating transaction signals so that an untrusted agent's security identifier is incorrectly decoded as a trusted one.
• Common attack patterns include intercepting and altering bus transactions to change the perceived identity of the sender.

• Security Impact:

• Direct consequences include unauthorized access to sensitive assets, data breaches, and potential modification of critical processes.
• Potential cascading effects involve further compromise of system integrity and escalation of privileges.
• Business impact could be significant, including loss of intellectual property, regulatory penalties, and reputational damage.

• Prevention Guidelines:

• Specific code-level fixes include implementing robust validation and error-checking mechanisms for security identifier decoding.
• Security best practices involve using layered security measures and ensuring comprehensive access control policies.
• Recommended tools and frameworks include static code analysis tools to detect potential decoding errors and hardware security modules to enforce secure transaction handling.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Not Language-Specific

Affected Technologies: Bus/Interface Hardware, Not Technology-Specific

Vulnerable Code Example

import base64

def decode_security_identifier(encoded_id):
    # Directly using base64 decode without validation can lead to incorrect decoding
    decoded_bytes = base64.b64decode(encoded_id)
    decoded_id = decoded_bytes.decode('utf-8')
    # Assuming the decoded value is a valid security identifier
    return decoded_id

# Example usage
encoded_id = 'c2VjdXJpdHlfdXNlcg=='  # base64 for 'security_user'
print(decode_security_identifier(encoded_id))

Vulnerability Explanation:

• The function decode_security_identifier directly decodes a base64-encoded string without validating its content. If the input is manipulated or malformed, it can lead to incorrect or unexpected decoding. This can potentially allow unauthorized access if the decoded identifier is used for access control, as the decoded result may not be a valid or expected security identifier.

How to fix Incorrect Decoding of Security Identifiers ?

Fixed Code Example

import base64
import re

def decode_security_identifier(encoded_id):
    # Validate if the input is a valid base64 string
    if not re.match(r'^[A-Za-z0-9+/=]+\$', encoded_id):
        raise ValueError("Invalid base64 input")

    try:
        # Using validate=True to ensure input is correctly padded and valid base64
        decoded_bytes = base64.b64decode(encoded_id, validate=True)
        decoded_id = decoded_bytes.decode('utf-8')

        # Check if the decoded identifier matches the expected format
        if not re.match(r'^[a-zA-Z0-9_]+\$', decoded_id):
            raise ValueError("Decoded identifier does not match expected format")

        return decoded_id
    except (base64.binascii.Error, ValueError) as e:
        # Log the error and handle it appropriately
        print(f"Decoding error: {e}")
        return None

# Example usage
encoded_id = 'c2VjdXJpdHlfdXNlcg=='  # base64 for 'security_user'
print(decode_security_identifier(encoded_id))

Fix Explanation:

• Input Validation: A regular expression is used to ensure the input string is a valid base64-encoded value. This prevents the function from processing malformed or malicious inputs.
• Base64 Decoding with Validation: The validate=True parameter in base64.b64decode ensures the input is correctly padded and is a valid base64 string.
• Error Handling: A try-except block is implemented to catch any decoding errors. This prevents the application from crashing due to unexpected input and allows for graceful error handling.
• Sanitization: After decoding, the identifier is checked against a regular expression to ensure it matches the expected format. This prevents misuse of incorrectly decoded identifiers and ensures that the decoded value is safe to use for security-sensitive operations.