Recently, a vulnerability was discovered in Firefox, Firefox ESR, and Thunderbird that could lead to a potentially exploitable crash. This vulnerability, dubbed CVE-2023-25751, can occur due to incorrect overwriting of JIT (Just-In-Time) code during the invalidation process when using an iterator. In this post, we'll discuss the vulnerability in detail, the affected versions, code snippets that demonstrate the issue, links to relevant references, and the possible exploit scenarios.

Description

Just-In-Time (JIT) is a compilation technique employed by JavaScript engines in browsers to enhance the performance and execution of JavaScript code. During the execution process, it's sometimes necessary to invalidate the generated JIT code to address memory-related issues or to optimize the code further. This invalidation process should be done meticulously, avoiding any inconsistencies or corruption of the live code.

However, in Firefox < 111, Firefox ESR < 102.9, and Thunderbird < 102.9, it was discovered that sometimes, when invalidating JIT code while following an iterator, the newly generated code could be overwritten incorrectly. This can potentially lead to crashes, with code execution exploitable by attackers.

Let's consider the following JavaScript code snippet

function vulnerableFunction() {
  for (const record of someIterator) {
    // ...
    invalidateJITFunction(record); // invalidate JIT code
    // ...
  }
}

In the above example, we can see that the function uses an iterator and invalidates JIT code for record. The issue here is that during the invalidation process, the newly generated code can be overwritten causing memory corruption and potentially exploitable crashes.

Original References

This vulnerability has been assigned CVE-2023-25751 and was initially reported and documented by the following security advisories:

1. Mozilla Foundation Security Advisory 2023-07: https://www.mozilla.org/en-US/security/advisories/mfsa2023-07/

2. Mozilla Foundation Security Advisory 2023-08: https://www.mozilla.org/en-US/security/advisories/mfsa2023-08/

3. Mozilla Foundation Security Advisory 2023-09: https://www.mozilla.org/en-US/security/advisories/mfsa2023-09/

Exploit Details

Given the nature of the vulnerability and its impact on the affected software, an attacker could potentially execute arbitrary code on the victim's system through the incorrect overwriting of JIT code.

Let's break down a possible exploit scenario

1. The attacker crafts a malicious web page containing JavaScript code designed to trigger the vulnerability.

The victim visits the malicious web page using a vulnerable version of Firefox or Firefox ESR.

3. The attacker's JavaScript code attempts to invalidate JIT code in such a way that the code is overwritten incorrectly, triggering a potentially exploitable crash.
4. If successful, the attacker could execute arbitrary code on the victim's system and potentially compromise the user's data and system security.

Mitigation and Conclusion

To address this vulnerability, it is crucial to update the affected software to the latest versions. For Firefox, you'll want to update to version 111 or later. For Firefox ESR and Thunderbird, ensure that you're using version 102.9 or newer.

Understanding the nature of the vulnerability and its potential exploits, coupled with vigilant security practices, can help you mitigate the risk associated with CVE-2023-25751, and ensure that your systems are protected against potentially harmful attacks.

Timeline

Published on: 06/02/2023 17:15:00 UTC
Last modified on: 06/08/2023 17:14:00 UTC