CVE-2026-117994 in Firefox
Summary
by MITRE • 10/27/2026
Use-after-free in the JavaScript: GC component. This vulnerability was fixed in Firefox 159 and Firefox ESR 153.6.
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Analysis
by VulDB Data Team • 10/27/2026
The identified vulnerability represents a critical memory management error within the garbage collection subsystem of the Mozilla Gecko engine, specifically affecting its JavaScript execution environment. As a use-after-free flaw, this defect occurs when the application attempts to access or manipulate a memory region that has already been deallocated and potentially reused for other purposes. In the context of browser-based JavaScript engines, such as SpiderMonkey which powers Firefox, precise control over object lifecycles is paramount because these objects often contain pointers to sensitive data structures including execution contexts, stack frames, and heap allocations. When the garbage collector incorrectly identifies an object as unreachable or prematurely reclaims its memory while active references still exist within the runtime environment, it creates a dangling pointer situation that violates fundamental memory safety principles.
From a technical perspective, this flaw typically arises during complex interactions between the JavaScript engine's tracing garbage collection mechanisms and specific script execution patterns. The vulnerability likely involves scenarios where an object is freed by the collector due to perceived lack of references, yet subsequent operations within the same thread or via asynchronous callbacks continue to reference that now-invalid memory address. This discrepancy can lead to undefined behavior ranging from minor data corruption to severe security breaches depending on how the attacker manipulates the heap state following the premature deallocation. The complexity lies in the non-deterministic nature of garbage collection, which makes reproducing and isolating such timing-dependent bugs particularly challenging for developers but highly exploitable by adversaries who can craft specific JavaScript payloads to trigger the race condition or logical error consistently.
The operational impact of this vulnerability is severe, as it allows for potential arbitrary code execution within the browser process sandbox. An attacker could construct a malicious web page containing specially crafted JavaScript that triggers the use-after-free condition during normal browsing activities such as loading dynamic content or executing third-party scripts. Successful exploitation enables the adversary to read sensitive information from memory, including cookies, session tokens, and potentially credentials stored in local storage, thereby compromising user privacy and account security. Furthermore, if combined with other vulnerabilities or through sophisticated heap spraying techniques, this flaw can facilitate full system compromise by bypassing modern browser mitigations like ASLR and DEP, allowing the execution of arbitrary shellcode that escapes the sandboxed environment to interact directly with the underlying operating system.
To mitigate risks associated with this vulnerability, immediate action is required to ensure all instances of Firefox are updated to version 159 or later, including the Extended Support Release branch at version 153.6. These updates contain specific patches that correct the reference counting logic and improve validation checks within the garbage collector to prevent access to freed memory regions. Organizations should enforce automated patch management policies to ensure rapid deployment of these fixes across all endpoints. Additionally, users are advised to maintain strict browsing hygiene by avoiding untrusted websites and utilizing browser extensions that block potentially malicious scripts or restrict execution contexts where possible. Security teams should also monitor for indicators of compromise related to JavaScript-based exploits in network traffic logs as a supplementary defense-in-depth measure while ensuring the underlying software stack remains current with vendor-recommended security updates aligned with CWE-416 standards for use-after-free vulnerabilities and ATT&CK techniques involving client-side code execution.