CVE-2026-117881 in Firefox
Summary
by MITRE • 10/27/2026
Use-after-free in the DOM: Core & HTML component. This vulnerability was fixed in Firefox 159, Firefox ESR 115.44, 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 Document Object Model core and HTML components of Mozilla Firefox browsers. Specifically classified as an use-after-free condition, this flaw occurs when the application continues to reference a memory block after it has been deallocated or freed by the system. In the context of browser rendering engines, such errors typically arise during complex DOM manipulation operations where elements are dynamically added, removed, or modified via JavaScript. If the internal pointers tracking these DOM nodes become desynchronized with the actual state of allocated memory, the engine may attempt to access data that has already been reclaimed by the operating system's garbage collector or memory manager. This scenario creates a window of opportunity for malicious actors to exploit the dangling pointer and execute arbitrary code within the context of the browser process.
From a technical perspective, this vulnerability aligns with CWE-416, which defines use-after-free as an error where software uses memory after it has been freed. The exploitation vector often involves crafting specific HTML structures or JavaScript sequences that trigger rapid allocation and deallocation cycles during page rendering. When the browser attempts to read from or write to the previously allocated address, it may interpret random data in that location as executable instructions or valid object properties. This can lead to a complete compromise of the user's system if the attacker successfully achieves arbitrary code execution with the privileges of the compromised process. The severity is heightened by the fact that DOM vulnerabilities are frequently reachable through standard web browsing activities, requiring no special configuration beyond visiting a maliciously crafted website.
The operational impact of this vulnerability extends beyond simple application crashes or denial of service conditions. While unexploited instances might result in browser instability or tab termination, successful exploitation allows for remote code execution without user interaction beyond initial page load. This capability enables attackers to install malware, steal sensitive credentials stored within the browser session, perform keylogging, or pivot into internal network environments if the victim is part of a corporate infrastructure protected by perimeter defenses that do not inspect encrypted web traffic thoroughly. The risk is particularly acute for users who frequently visit untrusted sites or engage in high-risk online activities where they cannot verify the integrity of third-party scripts and embedded content.
This flaw was addressed in Firefox version 159, as well as extended support releases including Firefox ESR 115.44 and Firefox ESR 153.6. The remediation strategy involved rigorous code auditing to ensure that all references to DOM nodes are properly invalidated or updated when the underlying memory is released. Developers likely implemented stricter checks during the garbage collection phase of the JavaScript engine to prevent dangling pointers from persisting in active execution contexts. Additionally, modern browser security mitigations such as heap hardening techniques and sandboxing mechanisms provide additional layers of defense by limiting the impact of any successful exploitation attempt on the host operating system.
To mitigate risks associated with this class of vulnerabilities, organizations should enforce strict update policies to ensure all endpoints are running patched versions of Firefox immediately upon release. Security teams should also consider implementing browser isolation technologies or containerization solutions that restrict the privileges granted to web content processes. Furthermore, deploying endpoint detection and response tools capable of monitoring for anomalous memory access patterns can help identify exploitation attempts in real-time. Regular security awareness training remains essential to reduce the likelihood of users interacting with malicious websites that may attempt to leverage such zero-day or recently patched vulnerabilities against their systems.