CVE-2026-74938 in Firefox
Summary
by MITRE • 08/18/2026
Mitigation bypass in the JavaScript: GC component. This vulnerability was fixed in Firefox 154 and Firefox ESR 153.1.
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Analysis
by VulDB Data Team • 08/18/2026
The identified security issue represents a critical failure within the garbage collection subsystem of Mozilla's JavaScript engine, SpiderMonkey. Garbage collection is a fundamental memory management technique used to automatically reclaim objects that are no longer referenced by the program. In this specific instance, the vulnerability stems from an improper handling state or logic error during the finalization phase of object lifecycle management. When the browser attempts to clean up unused memory, it fails to correctly validate references or update internal pointers before releasing resources. This flaw allows for a scenario where the garbage collector may prematurely free memory that is still actively being accessed by executing JavaScript code, leading to use-after-free conditions. Such errors are particularly dangerous because they bypass standard safety checks designed to prevent unauthorized access to freed memory regions.
The operational impact of this vulnerability is severe, as it can lead to arbitrary code execution with the privileges of the user running the browser. An attacker could craft a malicious webpage containing specially crafted JavaScript that triggers the garbage collection flaw during page load or interaction. By exploiting the race condition between object finalization and reference validation, the attacker can manipulate memory layout to achieve control over program flow. This typically involves overwriting function pointers or virtual table entries within freed objects, allowing for remote code execution on the victim's system. The vulnerability affects both standard Firefox releases and Extended Support Release versions prior to their respective updates, indicating a systemic issue in the core engine rather than an isolated edge case.
From a classification perspective, this flaw aligns with CWE-416, Use After Free, which describes situations where software continues to use memory after it has been freed. This often leads to crashes or arbitrary code execution depending on how the freed memory is reused. In terms of offensive security frameworks, this vulnerability facilitates techniques associated with MITRE ATT&CK Tactic TA0004, Privilege Escalation, and specifically relates to exploitation methods that leverage memory corruption for initial access or lateral movement within a compromised environment. The ability to bypass mitigation mechanisms suggests that existing sandboxing or exploit mitigations like ASLR or DEP may be circumvented if the attacker can reliably control heap contents through this use-after-free condition.
Mitigation has been addressed in Firefox version 154 and Firefox ESR 153.1, where developers have implemented stricter validation checks within the garbage collection logic to ensure that references are valid before memory is reclaimed. Users of affected versions must update their browsers immediately to close this security gap. In addition to updating software, organizations should enforce strict content security policies and restrict execution of untrusted scripts to reduce the attack surface. Monitoring for unusual browser behavior or unexpected network connections can also help detect potential exploitation attempts in real-time while patching efforts are completed across all endpoints.