CVE-2026-117919 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 manipulations where elements are dynamically added, removed, or modified via JavaScript execution. When the internal state tracking these objects becomes desynchronized with actual memory allocation states, the engine may attempt to access pointers that no longer point to valid data structures. This scenario creates a window of opportunity for malicious actors to exploit the dangling pointer by manipulating the freed memory region before it is reallocated for other purposes or overwritten by the operating system.
From a technical perspective, this flaw falls under CWE-416 which defines use-after-free vulnerabilities as conditions where software uses pointers that point to deallocated memory. The impact of such a vulnerability extends beyond simple application crashes; while a denial-of-service condition is possible if the browser handles the error gracefully by terminating the process, the primary risk lies in arbitrary code execution. By carefully crafting specific HTML and JavaScript payloads, an attacker can control what data is written into the freed memory space. This allows for precise manipulation of heap metadata or function pointers within the browser's internal structures. Consequently, this can lead to the execution of arbitrary shellcode with the privileges of the user running the browser, effectively compromising the entire system security posture if no additional sandboxing mechanisms are in place.
In terms of threat modeling and industry standards, this vulnerability aligns closely with MITRE ATT&CK technique T1203 which covers exploitation for client-side execution. Attackers typically deliver such exploits through malicious websites or compromised legitimate sites that have been injected with exploit code via cross-site scripting vulnerabilities elsewhere on the network. The browser acts as the attack vector, interpreting the malformed DOM operations and triggering the memory corruption flaw during rendering or layout calculation phases. This highlights the persistent challenge in web application security where complex interactions between HTML parsers, JavaScript engines, and garbage collectors create intricate surfaces for memory safety violations to occur.
The resolution of this issue was implemented in Firefox version 159 as well as specific maintenance releases including Firefox ESR 115.44 and Firefox ESR 153.6. These updates incorporate rigorous checks within the DOM implementation to ensure that pointers are invalidated immediately after memory deallocation, preventing any subsequent access attempts from succeeding. For organizations relying on Extended Support Release versions of Firefox, it is imperative to verify that systems have been updated to at least version 115.44 or 153.6 depending on their specific release channel configuration. Delaying these updates leaves endpoints vulnerable to sophisticated drive-by download attacks and targeted phishing campaigns designed specifically to leverage known browser vulnerabilities for initial access into corporate networks.
To mitigate the risk associated with such memory corruption flaws, administrators should ensure that automatic update mechanisms are enabled within Firefox deployments across all user workstations. Additionally, implementing strict content security policies can help reduce the attack surface by restricting where scripts and resources can be loaded from, thereby limiting the ability of external attackers to inject malicious DOM manipulation code into trusted pages. Security awareness training for end-users remains relevant as social engineering often serves as the initial vector that leads users to visit sites hosting these exploits. Regular vulnerability scanning and patch management cycles are essential components of a defense-in-depth strategy against browser-based attacks, ensuring that known issues like this use-after-free condition do not persist in production environments where they could be actively exploited by threat actors seeking system compromise.