A Pwn2Own SpiderMonkey JIT Bug: From Integer Range Inconsistency to Bound Check Elimination then RCE

An attacker was able to perform an out-of-bounds read or write on a JavaScript object by fooling range-based bounds check elimination. This vulnerability affects Firefox < 124.0.1.

This vulnerability allows remote attackers to execute arbitrary code on affected installations of Mozilla Firefox. User interaction is required to exploit this vulnerability in that the target must visit a malicious page or open a malicious file.

The specific flaw exists within the SpiderMonkey JIT compiler. The issue results from the lack of proper validation of user-supplied data, which can result in a write past the end of an allocated buffer. An attacker can leverage this vulnerability to execute code in the context of the current process at low integrity.

Introduction to CVE-2024-29943

In the ever-evolving landscape of cybersecurity, staying informed about potential vulnerabilities is crucial. One such recent vulnerability is CVE-2024-29943, which affects Mozilla Firefox’s SpiderMonkey JavaScript engine. This blog post aims to provide a comprehensive explanation of this vulnerability, how it operates, and the implications for users.

What is SpiderMonkey JIT?

SpiderMonkey is the JavaScript engine used by Mozilla Firefox. It includes a Just-In-Time (JIT) compiler that enhances performance by compiling JavaScript code into machine code at runtime. While JIT compilation significantly speeds up web browsing, it also introduces potential risks, especially if the code being executed is not properly sanitized.

Details of the Vulnerability

CVE-2024-29943 is a Remote Code Execution (RCE) vulnerability found in the SpiderMonkey JIT compiler. This vulnerability allows attackers to execute arbitrary code on a victim’s machine by exploiting a flaw in the way SpiderMonkey handles specific JavaScript operations. An attacker could potentially gain control over a system if the user visits a malicious website designed to exploit this flaw.

Impact and Mitigation

The impact of CVE-2024-29943 can be severe, as it allows for remote code execution, which can lead to unauthorized access, data theft, and more. Mozilla has released patches to address this vulnerability, and users are strongly advised to update their Firefox browsers to the latest version. Additionally, employing security best practices, such as using script-blocking extensions and avoiding untrusted websites, can mitigate the risks associated with this and similar vulnerabilities.

Conclusion

Understanding and addressing vulnerabilities like CVE-2024-29943 is essential for maintaining cybersecurity. By keeping your software up-to-date and practicing safe browsing habits, you can protect yourself from potential threats. Stay informed and stay secure.