CVE-2023-41936 is a security vulnerability affecting the Jenkins Google Login Plugin version 1.7 and earlier. This vulnerability arises from using a non-constant time comparison function when verifying if the expected and provided token values are equal. By exploiting this flaw, attackers can utilize statistical methods to potentially derive a valid token. This article delves into the details of the vulnerability, including a code snippet to elaborate the issue, original references, and suggestions to mitigate potential attacks.

CVE-2023-41936 Vulnerability Details

The Jenkins Google Login Plugin is popular among developers to enable authentication with Google accounts when logging into the Jenkins server. In versions 1.7 and earlier, the method used for comparing expected and provided tokens is not time-constant. It means that the time taken for the comparison is dependent on the number of characters that match in both tokens. Attackers can exploit this to perform timing attacks by analyzing how long it takes for the system to perform the comparison and make educated guesses about the token value.

Here's a code snippet illustrating the vulnerable function which uses a non-constant time comparison

boolean isEqual(String tokenA, String tokenB) {
    if (tokenA.length() != tokenB.length()) {
        return false;
    }
    int match = ;
    for (int i = ; i < tokenA.length(); i++) {
        if (tokenA.charAt(i) == tokenB.charAt(i)) {
            match++;
        }
    }
    return (match == tokenA.length());
}

As shown above, the function returns the result as soon as it detects a mismatched character. This non-constant time comparison becomes a potential security risk, making it easier for attackers to guess the token using statistical methods.

1. Jenkins Security Advisory: https://www.jenkins.io/security/advisory/2023-01-16/#SECURITY-2584
2. CVE-2023-41936 Description: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-41936

Exploit Details

The exploitation of this vulnerability requires attackers to have access to time measurements during token verification. They can then use statistical methods to exploit the non-constant time comparison, enabling them to guess tokens character by character. It is worth mentioning that such attacks require a significant amount of attempts and are not easily executed. However, it still poses a potential security risk.

Mitigation

The immediate solution to prevent the exploitation of the CVE-2023-41936 vulnerability is to update the Jenkins Google Login Plugin to version 1.8 or later, which implements a constant-time comparison function. Additionally, consider adding monitoring and rate-limiting mechanisms to detect and prevent brute force attacks and restrict the number of failed attempts.

Conclusion

CVE-2023-41936 is a relevant security vulnerability that poses a threat to Jenkins Google Login Plugin users. To ensure the security of authentication systems, developers must stay vigilant and keep their plugins up to date. In this case, updating the Jenkins Google Login Plugin to version 1.8 or later is crucial to prevent the potential exploitation of the non-constant time comparison function, as well as to keep the authentication system's integrity and users' data secured.

Timeline

Published on: 09/06/2023 13:15:00 UTC
Last modified on: 09/11/2023 17:53:00 UTC