CVE-2026-117909 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.
If you want to get best quality of vulnerability data, you may have to visit VulDB.
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 condition, this flaw occurs when the application attempts to access or manipulate a memory region that has already been deallocated and potentially reused by other processes. In the context of browser-based scripting engines like SpiderMonkey, which powers Firefox, such errors are particularly dangerous because they can lead to arbitrary code execution if an attacker can carefully craft malicious JavaScript payloads to control how freed memory is reallocated. The vulnerability was addressed in Firefox version 159 and Firefox Extended Support Release (ESR) version 153.6, marking a significant step toward stabilizing the browser's internal state management during complex script evaluations.
From a technical perspective, garbage collection systems are designed to automatically reclaim memory occupied by objects that are no longer referenced by running programs. However, if there is a race condition or logic error where a reference to an object persists after its underlying memory has been freed, any subsequent access to that pointer results in undefined behavior. In modern browsers, this often translates to the ability for malicious web content to read sensitive data from adjacent heap regions or overwrite function pointers and vtables. This mechanism is frequently exploited by attackers to bypass security mitigations such as Address Space Layout Randomization (ASLR) and Data Execution Prevention (DEP). The specific impact of this vulnerability lies in its potential to allow a remote attacker who hosts a specially crafted website to execute arbitrary code on the victim's system, effectively compromising the integrity and confidentiality of the user environment.
This type of flaw is commonly classified under CWE-416, which defines use-after-free vulnerabilities as errors resulting from referencing memory after it has been freed. In terms of offensive security frameworks, this vulnerability aligns with MITRE ATT&CK technique T1203, specifically the exploitation phase where attackers leverage software vulnerabilities to execute code on target systems. The attack vector typically involves social engineering or drive-by download tactics where a user is directed to a malicious site containing exploit code designed to trigger the garbage collection anomaly. Once triggered, the attacker gains a foothold that can be escalated through further exploits or used to install persistent malware, steal session cookies, or perform actions on behalf of the authenticated user.
Mitigation strategies primarily involve ensuring that all client systems are updated to the latest patched versions of Firefox and its ESR variants. Since this is a remote code execution vulnerability with no known workaround other than patching, organizations should prioritize deploying these updates across their desktop fleets. Additionally, security teams can implement browser hardening policies such as disabling JavaScript in untrusted zones or using content security policies that restrict the loading of external scripts from unknown origins. Monitoring for anomalous network traffic originating from local processes after visiting suspicious websites can also help detect potential exploitation attempts before significant damage occurs. Regular vulnerability scanning and patch management cycles are essential to maintaining resilience against these types of memory corruption flaws in web browsers.