In recent times, there have been various attacks on computer systems, exposing severe vulnerabilities. One such vulnerability, CVE-2024-0436, could potentially allow an attacker to brute-force the password for an instance in single-user password protection mode via a timing attack due to the linear nature of the !== used for comparison. This article aims to discuss this vulnerability in detail, providing code snippets, links to original references, and exploit details.

Vulnerability Details

The vulnerability lies in the implementation of the password hashes comparison algorithm. When two strings are compared using the !== JavaScript operator, the comparison is made character by character in a linear fashion. This can lead a savvy attacker to analyze the time it takes to complete the operation and, ultimately, deduce how many characters in the password match.

An example of a vulnerable code snippet would be:

if (hash_user_input !== stored_hash) {
    return false; // Access Denied
}
// Access Granted

In this example, the longer it takes to return Access Denied, the more characters match in the hash. An attacker can exploit this timing inconsistency to carry out a brute-force attack and eventually find the matching hash.

Exploit Details

The attacker can send multiple requests, varying only one character at a time, and analyzing how long it takes for the server to return a response. As the server matches each character, the longer it takes for the server to process the request, indicating that the character is part of the correct password. By iterating through all possible characters, an attacker can construct the correct password relatively quickly.

While this type of attack isn't foolproof because of the non-constant nature of the request overhead, the attack can significantly speed up the brute-force process.

Mitigation Strategies

To combat this attack, developers are encouraged to replace the linear comparison !== with a constant-time comparison function, rendering it ineffective for a malicious individual to exploit the discrepancies in processing time.

One possible solution to prevent this type of timing attack vulnerability is using a constant-time comparison function such as the following:

function constant_time_compare(a, b) {
    if (a.length !== b.length) {
        return false;
    }
    let result = ;
    for (let i = ; i < a.length; i++) {
        result |= a.charCodeAt(i) ^ b.charCodeAt(i);
    }
    return result === ;
}

Incorporating this constant-time comparison function into your implementation ensures that the time taken for comparison remains constant, whether the passwords match completely or not, making the timing attack less reliable to execute.

For more information on this vulnerability, please refer to the following resources

1. OWASP - Using constant time algorithm
2. Common Weakness Enumeration - Password Timing Attack

Conclusion

Timing attacks, like the one discussed in this article, are a significant threat to online security. Developers must be always vigilant to these risks and take the necessary steps to mitigate them. By using constant-time algorithms to compare sensitive data like passwords, the possibility of leakage through timing attacks can be reduced, making systems more secure.

Timeline

Published on: 02/26/2024 16:27:50 UTC
Last modified on: 02/26/2024 16:32:25 UTC