CVE-2024-7521 in Firefox
Summary
by MITRE • 08/06/2024
Incomplete WebAssembly exception handing could have led to a use-after-free. This vulnerability affects Firefox < 129, Firefox ESR < 115.14, and Firefox ESR < 128.1.
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Analysis
by VulDB Data Team • 03/15/2025
The vulnerability identified as CVE-2024-7521 represents a critical flaw in Firefox's WebAssembly exception handling mechanism that could potentially lead to arbitrary code execution through use-after-free conditions. This issue specifically impacts Firefox versions prior to 129, Firefox ESR versions prior to 115.14, and Firefox ESR versions prior to 128.1, making it a widespread concern across multiple release channels. The flaw resides in how Firefox processes WebAssembly exceptions, creating a scenario where memory that has been freed could still be accessed by subsequent operations.
WebAssembly exception handling in Firefox involves complex memory management operations where exception frames are created and destroyed during program execution. The incomplete implementation fails to properly track and manage the lifecycle of these exception objects, particularly when exceptions are thrown and caught within WebAssembly modules. This incomplete tracking allows for scenarios where the memory allocated to exception objects becomes available for reuse before all references to those objects are properly cleared, creating the conditions for use-after-free vulnerabilities.
The technical impact of this vulnerability extends beyond simple memory corruption, as it provides potential attack vectors for remote code execution. When a WebAssembly module triggers an exception that is not properly handled, the memory management system may prematurely free objects that are still referenced elsewhere in the program execution flow. This can result in attackers being able to manipulate the freed memory to execute arbitrary code, particularly when combined with other exploitation techniques such as heap spraying or return-oriented programming. The vulnerability is particularly concerning given that WebAssembly modules can be embedded in web pages, making exploitation possible through malicious websites without requiring user interaction beyond visiting the page.
From a cybersecurity perspective, this vulnerability maps to CWE-416, which specifically addresses use-after-free conditions, and aligns with ATT&CK techniques related to code injection and memory corruption. The flaw demonstrates how complex virtual machine implementations can introduce subtle security issues in memory management systems, particularly when dealing with exception handling mechanisms that span multiple execution contexts. Organizations using affected Firefox versions should prioritize immediate patching to prevent potential exploitation, as the vulnerability could be leveraged in advanced persistent threat campaigns or zero-day attacks targeting enterprise environments.
Mitigation strategies for this vulnerability include immediate deployment of patched Firefox versions, implementation of web application firewalls to monitor for suspicious WebAssembly activity, and enhanced monitoring of browser memory usage patterns. Security teams should also consider implementing sandboxing measures and network segmentation to limit the potential impact of successful exploitation attempts. Regular security assessments of web applications that utilize WebAssembly should be conducted to identify and remediate similar vulnerabilities in custom implementations. The vulnerability underscores the importance of comprehensive testing of exception handling mechanisms in complex software systems and highlights the need for continuous security validation of virtual machine implementations.