CVE-2023-40343 is a security vulnerability related to Jenkins Tuleap Authentication Plugin 1.1.20 and earlier versions. The plugin, which is used for authenticating Jenkins users against the Tuleap server, contains a non-constant time comparison function used for validating an authentication token. The vulnerability allows attackers to use statistical methods to obtain a valid authentication token, consequently gaining unauthorized access to the Jenkins server and its resources.

In this article, we will discuss the details of this vulnerability, its impact on the security of Jenkins servers using the affected plugin, and the potential exploitation methods. We will also provide code snippets to understand the inner workings and provide recommendations for mitigating the risk posed by this vulnerability. Lastly, we will link to original references for further in-depth reading.

Vulnerability Details

Affected Product: Jenkins Tuleap Authentication Plugin
Affected Versions: 1.1.20 and earlier
CVE ID: CVE-2023-40343
Severity: Medium
Attack Vector: Remote
Authentication: Not Required

Code Snippets

We will now analyze the code snippet that creates a non-constant time comparison function inside the Tuleap Authentication Plugin. Below is a simplified version of the vulnerable comparison function:

boolean isValidToken(String token, String validToken) {
  if (token.length() != validToken.length()) {
    return false;
  }

  int equalChars = ;
  for (int i = ; i < token.length(); i++) {
    if (token.charAt(i) == validToken.charAt(i)) {
      equalChars++;
    }
  }

  return equalChars == token.length();
}

In the above code snippet, isValidToken is the method that checks if the provided token is equal to the validToken. The function first checks if the lengths of both strings are equal and then iterates over both strings comparing each character. While the overall method appears to be correct, it is not constant-time in nature.

Exploitation Details

The non-constant time comparison function makes the server vulnerable to timing-based side-channel attacks. An attacker can obtain a valid token by continuously sending authentication requests with different token values while monitoring the time taken by the server to respond. The server response time will be slightly longer when the provided token has more matching characters than a completely incorrect token.

By iteratively modifying one character of the token at a time and measuring the response times, an attacker can eventually identify a valid authentication token and gain unauthorized access to the server.

Mitigation and Recommendations

To mitigate the vulnerability, it is strongly recommended to upgrade the Jenkins Tuleap Authentication Plugin to version 1.1.21 or later. The fixed versions of the plugin employ a constant-time comparison function to validate authentication tokens, eliminating the risk of timing-based side-channel attacks.

Jenkins Plugin Manager: Find the Tuleap Authentication Plugin and select "Upgrade"

- Official Plugin Repository: https://plugins.jenkins.io/tuleap-api/

In addition to upgrading the plugin, it is crucial to follow general best practices for securing your Jenkins server, such as applying regular security updates, restricting access to the server, and monitoring for suspicious activity.

Original References

We encourage readers to explore the following resources for additional information on the vulnerability, and remediation:

1. Jenkins Security Advisory: https://www.jenkins.io/security/advisory/2023-01-12/#SECURITY-2859
2. Tuleap Authentication Plugin Release Notes: https://plugins.jenkins.io/tuleap-api/#releases
3. CVE Details: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-40343

Conclusion

CVE-2023-40343 represents a significant vulnerability in Jenkins Tuleap Authentication Plugin 1.1.20 and earlier versions. It highlights the importance of constant-time comparisons for secure token validation and serves as a reminder to developers to consider timing attacks while implementing authentication mechanisms. By staying updated with the latest security advisories and following best practices, administrators can minimize the risk posed by such vulnerabilities and safeguard their Jenkins server and its resources.

Timeline

Published on: 08/16/2023 15:15:00 UTC
Last modified on: 08/18/2023 20:04:00 UTC