A newly discovered vulnerability, identified under the code CVE-2023-25739, has been found in Firefox (versions prior to 110), Thunderbird (versions prior to 102.8), and Firefox ESR (versions prior to 102.8). This vulnerability is a result of module load requests that failed, not being properly checked to determine if they were cancelled. Consequently, this led to a Use-After-Free vulnerability in the ScriptLoadContext component. In this post, we will go over the vulnerability in detail, provide a code snippet demonstrating the flaw, and links to the original references. Furthermore, we will discuss the potential exploitation of this vulnerability and steps to mitigate any damage.

Vulnerability Details

The failure to check if module load requests were cancelled, coupled with how ScriptLoadContext was handling such cases, led to a Use-After-Free situation. Use-After-Free is a memory corruption vulnerability that occurs when a program continues to utilize a resource (such as memory) after it has been freed or deallocated, potentially allowing an attacker to gain control of the affected system.

The following code snippet demonstrates the issue with the ScriptLoadContext component

// ...
ScriptLoadContext::ScriptLoadContext(...) {
  // ...
  if (failedModuleLoad) {
    // MISSING: Check if the module load request was cancelled.
    mIsModuleRequest = true;
  } else {
    mIsModuleRequest = aScript->IsModule();
  }
}
// ...

As seen above, when the failedModuleLoad flag is set, the program should verify whether the module load request has been cancelled or not.

1. CVE-2023-25739 - Mozilla Security Advisory
2. Bugzilla - Bug 1739519 - Use-after-free in ScriptLoadContext

Exploit Details

If a malicious actor were to successfully exploit this vulnerability, they would potentially be able to execute arbitrary code within the scope of the affected application. Furthermore, this could lead to unauthorized access to sensitive information, manipulation of the application's data, or even a complete system compromise.

Mitigation Steps

To protect against this vulnerability, it is crucial to update Firefox, Thunderbird, and Firefox ESR to the latest available versions:

For Firefox ESR users, update to version 102.8 or later.

Users should ensure they keep their software up-to-date and apply security patches as soon as they are released.

Conclusion

CVE-2023-25739 highlights the importance of thoroughly inspecting module load requests, ensuring they are cancelled when necessary to prevent Use-After-Free vulnerabilities. By updating the vulnerable software and maintaining a proactive approach to security, users can safeguard their systems against potential exploitation of this vulnerability.

Timeline

Published on: 06/02/2023 17:15:00 UTC
Last modified on: 06/08/2023 16:15:00 UTC