CVE-2026-109725 in Firefox
Summary
by MITRE • 10/13/2026
Use-after-free in the DOM: Core & HTML component. This vulnerability was fixed in Firefox 158, Firefox ESR 115.43, and Firefox ESR 153.5.
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Analysis
by VulDB Data Team • 10/13/2026
The identified vulnerability represents a critical memory management error within the Document Object Model (DOM) implementation of the Core and HTML components in Mozilla Firefox browsers. Specifically classified as an use-after-free condition, this flaw occurs when the browser retains a reference to a DOM element or object after its underlying memory has been deallocated by the garbage collector or explicit cleanup routines. In complex web environments where dynamic content is frequently added, removed, or modified via JavaScript, the internal state tracking of these objects can become desynchronized from their actual lifecycle in memory. When an attacker crafts a malicious webpage that triggers this specific sequence of events, they can cause the browser to access freed memory locations as if they were still valid and allocated. This discrepancy between logical object existence and physical memory allocation is a classic example of CWE-416, which describes situations where software continues to use pointers after freeing them, leading to undefined behavior that attackers can exploit for malicious purposes.
The operational impact of this vulnerability extends beyond simple application instability or crashes. While unexploited instances may result in denial-of-service conditions due to segmentation faults or access violations, the primary security concern lies in its potential for remote code execution. By carefully manipulating memory layouts and heap structures through repeated allocations and deallocations, an attacker can achieve arbitrary read/write primitives. This capability allows them to overwrite function pointers or return addresses within the browser process, effectively hijacking control flow to execute arbitrary shellcode on the victim's system. Such exploits are particularly dangerous because they target the client-side rendering engine, meaning no server-side interaction is required beyond hosting a malicious webpage that the user visits. The attack vector aligns with ATT&CK technique T1203, which covers exploitation for browser or application execution, highlighting how web-based vulnerabilities serve as initial access vectors in broader cyber attacks.
Mitigation strategies primarily rely on timely software updates and defensive coding practices within the browser engine itself. For end-users, upgrading to Firefox version 158, Firefox Extended Support Release (ESR) version 115.43, or ESR version 153.5 is essential as these releases contain patches that enforce stricter memory safety checks during DOM manipulation operations. These updates likely introduce additional validation steps before dereferencing pointers to ensure the target object has not been freed. From a defensive posture perspective, organizations should implement browser isolation technologies and content security policies (CSP) to restrict inline scripts and untrusted sources, thereby reducing the attack surface available for triggering such memory corruption bugs. Additionally, enabling advanced heap protection mechanisms like ASLR and DEP helps mitigate the success rate of exploitation attempts by randomizing memory addresses and preventing code execution in data regions, providing a critical layer of defense even if similar vulnerabilities exist in other components or future releases.