CVE-2026-117936 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 parsing components of Mozilla Firefox browsers. Specifically classified as an use-after-free condition, this flaw occurs when the browser retains a reference to a DOM object or node that has already been deallocated from memory due to prior operations such as removal, replacement, or garbage collection cycles. In complex web environments where dynamic content manipulation is frequent, particularly through JavaScript frameworks that heavily interact with the DOM tree structure, the likelihood of triggering this race condition increases significantly. The vulnerability stems from a failure in the internal reference counting mechanism or pointer invalidation logic within the browser engine's C++ codebase, allowing execution to proceed against freed memory addresses rather than detecting and aborting the operation safely.
From a technical perspective, use-after-free vulnerabilities are among the most dangerous classes of software defects because they provide attackers with precise control over heap layout and arbitrary read-write primitives in many scenarios. When an attacker can manipulate the timing or sequence of DOM operations to free a node while another part of the browser still holds a dangling pointer to it, subsequent access to that pointer may result in reading sensitive data from adjacent memory regions or writing malicious payloads into executable code segments. This capability effectively bypasses modern memory safety protections such as ASLR and DEP if exploited correctly, leading to arbitrary code execution with the privileges of the user running the browser process. The specific components involved, Core and HTML parsing modules, are central to rendering web pages, meaning that simply visiting a maliciously crafted webpage could trigger the vulnerability without requiring any additional user interaction beyond initial page load or standard DOM manipulation events.
The operational impact of this flaw is severe, potentially allowing remote attackers to execute arbitrary code on the victim's system by crafting specific HTML and JavaScript payloads designed to exploit the timing window between memory deallocation and subsequent access. This could lead to full compromise of the end-user machine, including theft of sensitive information such as cookies, session tokens, passwords stored in browser profiles, or corporate data accessed through web applications. Furthermore, because this vulnerability exists within widely used enterprise browsers like Firefox ESR versions 153.6 and 115.44, it poses a significant risk to organizations relying on these stable releases for their security posture. Attackers often target such vulnerabilities in zero-day exploits or supply chain attacks where the browser is forced to render untrusted content generated by compromised websites or phishing campaigns.
To mitigate this risk, immediate patching is required as addressed in Firefox version 159 and the respective Extended Support Release versions 115.44 and 153.6. Organizations should enforce automated update policies to ensure all endpoints are running these patched versions promptly. Additionally, implementing strict Content Security Policy headers can help reduce the attack surface by restricting inline script execution and limiting sources from which scripts may be loaded, thereby reducing the likelihood of successful exploitation even if a similar vulnerability were present in future builds. From a development standpoint, this incident reinforces the importance of rigorous static analysis tools focused on memory safety issues like CWE-416 use-after-free during code reviews for browser engine components. Security teams should also monitor ATT&CK techniques related to client-side execution and privilege escalation via software vulnerabilities to detect potential exploitation attempts in network traffic or endpoint telemetry data before full patch deployment is achieved across all systems.