CVE-2026-117949 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 browser's rendering engine attempts to access or manipulate a DOM element that has already been deallocated from system memory. In complex web environments where dynamic content is frequently added, removed, or modified via JavaScript, the internal state tracking mechanisms may fail to correctly invalidate references to these elements before they are freed. This discrepancy allows maliciously crafted web pages to trigger operations on stale pointers, leading to undefined behavior within the browser process. Such vulnerabilities are particularly dangerous because they can often be exploited to achieve arbitrary code execution with the privileges of the user running the application, effectively bypassing standard security boundaries and compromising system integrity.
From a technical perspective, this flaw aligns closely with Common Weakness Enumeration identifier CWE-416, which defines use-after-free as accessing memory after it has been freed without ensuring proper reallocation or nullification of pointers. The vulnerability resides in the core parsing and rendering logic that handles HTML structure updates during runtime interactions. When a script modifies the DOM tree by removing nodes while other parts of the code still hold references to those same nodes, the underlying C++ objects may be destroyed prematurely. If subsequent operations attempt to read or write through these dangling pointers, it can result in memory corruption. This corruption can manifest as crashes causing denial of service, but more critically, it provides an attack surface for heap exploitation techniques that allow attackers to overwrite function pointers or vtable entries within the browser's process space.
The operational impact of this vulnerability is severe, posing a significant risk to end-users who visit maliciously designed websites. An attacker could construct a webpage containing specific JavaScript payloads and HTML structures engineered to trigger the race condition between DOM modification and memory deallocation. Successful exploitation would allow the execution of arbitrary code on the victim's machine, potentially leading to full system compromise including data theft, installation of malware, or use as part of a botnet. Given that Firefox is widely used for sensitive activities such as online banking and corporate communications, this vulnerability represents a high-severity threat vector requiring immediate attention from security teams and users alike.
This issue has been addressed in recent updates to the Mozilla browser family, specifically fixed in Firefox version 159, Firefox Extended Support Release (ESR) version 115.44, and Firefox ESR version 153.6. These patches likely involve rigorous validation of object lifecycles within the DOM implementation, ensuring that references are properly invalidated or managed through smart pointer mechanisms to prevent access after deallocation. To mitigate this risk, organizations should enforce strict update policies for all endpoints running affected browser versions. Users must ensure their browsers are updated immediately upon release of these patches. Additionally, deploying content security policies and restricting script execution on untrusted domains can provide an additional layer of defense by limiting the ability of external scripts to manipulate DOM structures in ways that might trigger such memory errors.
In terms of threat intelligence frameworks, this vulnerability maps to MITRE ATT&CK techniques related to initial access and privilege escalation via browser exploitation. Attackers frequently leverage use-after-free bugs as part of drive-by download campaigns or targeted spear-phishing efforts where the primary goal is code execution rather than simple data exfiltration. Security analysts should monitor for indicators of compromise associated with exploit kits that target known vulnerabilities in web rendering engines, particularly those involving DOM manipulation and memory corruption patterns consistent with CWE-416 classifications. Continuous monitoring and rapid patch deployment remain the most effective strategies against such high-severity browser vulnerabilities.