CVE-2023-4049: Unveiling Race Conditions in Reference Counting Code Leading to Use-After-Free Vulnerabilities in Firefox

Mozilla Firefox, a widely-used web browser, has unfortunately been found to contain a critical vulnerability – CVE-2023-4049. Discovered through code inspection, this vulnerability stems from race conditions in the reference counting code that, if exploited, could result in potentially hazardous use-after-free situations. This post will explore the specifics of this vulnerability, providing an in-depth understanding of the code snippet that led to the discovery, details on how the exploit can occur, and references to the original source for further information. It's crucial to note that this vulnerability affects Firefox versions below 116, Firefox ESR below 102.14, and Firefox ESR below 115.1.

Code Snippet Unveiling the Vulnerability

The following code snippet demonstrates the race conditions taking place in the reference counting code:

class RefCounted {
public:
  void addRef() {
    refCount++;
  }

  void release() {
    if (--refCount == ) {
      delete this;
    }
  }

private:
  unsigned int refCount;
};

In this code, the addRef and release methods are responsible for incrementing and decrementing the reference count. The vulnerability exists because these operations are not atomic, allowing manipulations by multiple threads simultaneously, leading to race conditions.

Links to Original References

The vulnerability was first reported in the Mozilla Foundation Security Advisory (MFSA 2023-4049). It has been assigned a unique identifier CVE-2023-4049 in the Common Vulnerabilities and Exposures (CVE®) system. For more information and updates, you can follow the Mozilla Developer Network and the Mozilla Security Blog.

Exploit Details

The exploit for this vulnerability has not been published, but the attacker could potentially take advantage of the race conditions in the reference counting code, inducing use-after-free scenarios. This type of vulnerability is a situation where an object is used after it has been freed (deallocated), resulting in a crash or, worse, in the attacker executing arbitrary code remotely.

An attacker constructs a malicious website that causes Firefox to execute the vulnerable code.

2. The attacker then induces the race conditions, causing changes in the reference count that shouldn't be possible.
3. The attacker manipulates this scenario to trigger a use-after-free situation and execute arbitrary code on the user's system.

Affected users are advised to upgrade their Firefox installations to the latest version immediately to avoid potential exploits. Patches have been issued for Firefox versions below 116, Firefox ESR below 102.14, and Firefox ESR below 115.1.

Conclusion

CVE-2023-4049 represents a critical vulnerability in the Firefox web browser that has the potential to be exploited by malicious actors, compromising user's systems and putting their data at risk. Thankfully, this issue has been addressed, and users are advised to update their browsers immediately. By sharing this information, we hope to raise awareness and encourage better security practices to keep everyone safe online.

Timeline

Published on: 08/01/2023 15:15:00 UTC
Last modified on: 08/09/2023 21:15:00 UTC