CVE-2026-117953 in Firefox
Summary
by MITRE • 10/27/2026
Use-after-free in the DOM: Core & HTML component. This vulnerability was fixed in Firefox 159 and Firefox ESR 153.6.
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Analysis
by VulDB Data Team • 10/27/2026
The identified security flaw represents a critical memory management error within the Document Object Model core and HTML components of Mozilla Firefox, specifically classified as an use-after-free vulnerability. In software engineering terms, this type of defect occurs when a program continues to use a pointer after it has been freed from memory allocation. Within the context of browser internals, the DOM serves as the structural backbone for web pages, translating HTML markup into a tree-like structure that scripts and rendering engines interact with. When an object within this structure is deallocated but references to it remain active in other parts of the application logic, accessing those dangling pointers leads to undefined behavior. This specific instance was addressed in Firefox version 159 and Firefox Extended Support Release (ESR) version 153.6, indicating that prior versions were susceptible to exploitation through crafted web content or malicious scripts interacting with DOM elements.
From a technical perspective, use-after-free vulnerabilities are particularly dangerous because they can lead to arbitrary code execution under the control of an attacker. The vulnerability likely stems from a race condition or improper lifecycle management where memory is released prematurely while still being referenced by event handlers, asynchronous callbacks, or rendering processes. An attacker could construct a malicious webpage that triggers specific DOM manipulations designed to free an object and then immediately access it before the garbage collector or system clears the reference. This allows the attacker to read sensitive data from the freed memory region or overwrite adjacent heap structures with controlled values. Such overwrites can corrupt internal browser state, potentially leading to crashes or more severe outcomes like sandbox escapes if the corrupted data influences security-critical decision paths within the browser engine.
The operational impact of this vulnerability is significant for end-users who browse untrusted websites or visit pages containing complex dynamic content. Successful exploitation could allow a remote attacker to execute arbitrary code on the victim's system, effectively compromising the integrity and confidentiality of the user environment. This aligns with Common Weakness Enumeration (CWE) identifier CWE-416, which defines use-after-free as a weakness where memory is freed but still referenced. Furthermore, in terms of attack vectors, this vulnerability facilitates techniques associated with MITRE ATT&CK tactic TA0002 Execution and potentially TA0005 Defense Evasion if used to bypass security controls like sandboxing mechanisms. The ability to execute code remotely via the browser engine makes it a high-priority target for drive-by download attacks or phishing campaigns that rely on exploiting browser flaws rather than user interaction alone.
Mitigation strategies primarily involve updating the browser software to versions where this flaw has been patched, specifically Firefox 159 and later, as well as Firefox ESR 153.6 and subsequent updates. For organizations managing large fleets of browsers, ensuring that automatic update policies are enabled is crucial to prevent exposure during the window between vulnerability disclosure and patch deployment. Additionally, users should employ browser hardening techniques such as disabling JavaScript on untrusted sites or using extensions that restrict DOM manipulation capabilities where feasible. Security teams should monitor for indicators of compromise related to memory corruption crashes in Firefox processes and ensure that endpoint detection systems are configured to flag unusual heap activity patterns associated with exploitation attempts. Regular patch management remains the most effective defense against these types of logic-based vulnerabilities inherent in complex software architectures like web browsers.