CVE-2026-117895 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 • 10/28/2026
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 application attempts to access or dereference a pointer that has already been deallocated by the system's garbage collector or explicit memory freeing routines. In the context of browser engines like Gecko, which handle complex DOM tree manipulations and HTML parsing in real-time during page rendering, such errors typically arise from race conditions between asynchronous JavaScript execution and synchronous layout updates, or from incorrect reference counting where an object is destroyed while still being referenced by another active component within the document structure.
From a technical perspective, this vulnerability falls under CWE-416, which defines use-after-free as a situation where software uses memory after it has been freed, leading to undefined behavior that can be exploited for malicious purposes. The attack vector generally involves an attacker crafting a specific HTML or JavaScript payload designed to trigger the premature deallocation of a DOM node while retaining a reference to that same node elsewhere in the script execution context. When the browser subsequently attempts to interact with this dangling pointer—whether by reading its properties, modifying its attributes, or triggering event handlers—the memory it points to may have been reallocated for other purposes or marked as free but not yet zeroed out. This discrepancy allows an attacker to read sensitive data from adjacent heap regions or write arbitrary values into the freed memory space.
The operational impact of this vulnerability is severe, potentially leading to remote code execution with the privileges of the user running the browser application. By carefully controlling the contents written to the reused memory block and subsequently triggering specific operations on it, a skilled attacker can manipulate control flow data structures such as function pointers or virtual table entries. This manipulation enables the injection and execution of arbitrary machine code within the context of the Firefox process. Such an exploit could allow for full system compromise if combined with other vulnerabilities that bypass browser sandboxing mechanisms, although even in isolation, it poses a significant risk to user privacy and data integrity by facilitating unauthorized access to cookies, session tokens, and locally stored credentials.
This type of memory corruption flaw is frequently associated with ATT&CK technique T1203, which covers exploitation for client execution, as well as techniques related to process injection if the exploit leverages native code capabilities within the browser's multi-process architecture. The vulnerability was addressed in Firefox version 159 and extended support release versions 115.44 and 153.6 through rigorous memory safety improvements, likely involving enhanced bounds checking, improved reference counting logic for DOM nodes, or the adoption of safer memory management patterns within the Gecko engine to prevent dangling pointers from being dereferenced during complex document manipulation tasks.
To mitigate the risks associated with this class of vulnerabilities, organizations and individual users must ensure that all instances of Firefox are updated to the latest stable version containing these security patches. Since use-after-free bugs can be difficult to detect without specialized debugging tools like AddressSanitizer or Valgrind, proactive defense relies heavily on keeping software up-to-date rather than relying solely on user behavior. Additionally, employing browser hardening techniques such as disabling unnecessary plugins and scripts, utilizing strict content security policies where applicable, and running browsers in sandboxed environments can reduce the attack surface available to potential exploiters attempting to leverage memory corruption flaws for unauthorized access or code execution.