CVE-2021-4240: Predictable Algorithm in Random Number Generator Vulnerability Found in PHP Server Monitor

A security vulnerability (CVE-2021-4240) was recently discovered in the phpservermon, a popular open-source tool used for monitoring websites and services. Herein, we will provide an in-depth explanation of the issue, relevant code snippets, links to original references, exploit details, and recommendations on how to patch this vulnerability.

Vulnerability Overview

The vulnerability in question was classified as problematic and primarily affects the generatePasswordResetToken function, found within the src/psm/Service/User.php file. The weakness stems from the use of a predictable algorithm in the random number generator, which may potentially be exploited by malicious actors to compromise the security of the phpservermon tool.

The identifier VDB-213717 was assigned to this vulnerability.

Exploit Details

The issue originates from the inadequate level of entropy used in the generatePasswordResetToken function of the src/psm/Service/User.php file, which could be manipulated by an attacker to predict the generated tokens. This weakness can be exploited remotely, and upon successful manipulation, the attacker may be granted unauthorized access to the user's password reset functionality.

Here is a code snippet from the vulnerable function generatePasswordResetToken in the src/psm/Service/User.php file:

public function generatePasswordResetToken($user_id) {
    $token = md5(uniqid(rand(), true));
    // ... remaining code ...
    return $token;
}

As we can see, the generatePasswordResetToken function utilizes the md5, uniqid, and rand functions to create a unique token. However, the rand function is known for its predictability, which ultimately results in a weak token generation mechanism.

Patch Details

The issue has been publicly disclosed. The developers of phpservermon have released a patch to address this vulnerability. The patch's name is 3daa804d5f56c55b3ae13bfac368bb84ec632193. Users are highly recommended to apply this patch to their phpservermon installations in order to protect their systems from potential exploits related to this vulnerability.

You can find the patch as a commit on the phpservermon GitHub repository: 3daa804d5f56c55b3ae13bfac368bb84ec632193

Conclusion

In conclusion, the CVE-2021-4240 vulnerability found in phpservermon poses a potential security risk to users of the tool. By understanding the nature of the security issue and applying the suggested patch, users can protect their systems from possible exploits. It is crucial for developers and users of open-source tools to be vigilant when utilizing third-party code, as even seemingly minor weaknesses can result in significant security breaches.

Timeline

Published on: 11/15/2022 23:15:00 UTC
Last modified on: 11/18/2022 19:51:00 UTC