CVE-2026-74944 in Firefox
Summary
by MITRE • 08/18/2026
Use-after-free in the DOM: Core & HTML component. This vulnerability was fixed in Firefox 154, Firefox ESR 140.14, and Firefox ESR 153.1.
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Analysis
by VulDB Data Team • 08/18/2026
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 retains a reference to a DOM element or related data structure after that object has been deallocated from system memory. In complex web environments where dynamic content is frequently manipulated via JavaScript, such errors can arise if event handlers or internal references are not properly updated during node removal or document restructuring operations. This specific instance was addressed in Firefox version 154 as well as the extended support releases ESR 140.14 and ESR 153.1, indicating that both current user bases and enterprise environments relying on stable release channels were affected until these patches were applied.
From a technical perspective, use-after-free vulnerabilities are among the most dangerous classes of memory corruption bugs because they allow an attacker to control how freed memory is interpreted by the application. When the browser attempts to access the dangling pointer after the underlying object has been destroyed, it may read stale data or write to arbitrary memory locations depending on what new allocation occupies that space in the heap. This lack of proper bounds checking and lifecycle management within the DOM implementation creates a scenario where maliciously crafted web pages can trigger these conditions through specific sequences of node manipulation events. The vulnerability falls under CWE-416, which defines use after free as referencing memory after it has been freed, leading to unpredictable behavior that is difficult to debug without specialized instrumentation tools like AddressSanitizer or Valgrind.
The operational impact of this flaw extends far beyond simple application crashes or denial-of-service scenarios. While a crash might be the immediate observable symptom for an average user, sophisticated attackers can leverage use-after-free conditions in browser engines to achieve arbitrary code execution with the privileges of the current user. By carefully crafting heap layouts and exploiting race conditions between allocation and deallocation phases, it is possible to overwrite function pointers or virtual table entries within the browser process. This capability aligns directly with MITRE ATT&CK technique T1203, which covers exploitation for client-side execution, allowing threat actors to install malware, exfiltrate sensitive data such as cookies and session tokens, or pivot into internal network segments if the victim is part of a corporate environment. The severity is further amplified by the ubiquity of Firefox in enterprise deployments where ESR versions are mandated for stability.
Mitigation strategies primarily rely on timely patch management to ensure that all client systems are running browser versions 154 and above, or the respective ESR patches mentioned. For organizations unable to immediately update due to compatibility testing requirements, network-level controls such as web application firewalls can be configured to detect and block known exploit patterns associated with DOM manipulation anomalies, although this is less effective against zero-day variants. Developers integrating Firefox-based applications should also ensure that their own code adheres strictly to memory safety principles by avoiding manual management of DOM references where possible and utilizing modern JavaScript frameworks that handle lifecycle events more robustly. Regular security audits focusing on dynamic content handling and the implementation of strict Content Security Policies can further reduce the attack surface, limiting the ability of injected scripts to perform complex heap grooming operations necessary for successful exploitation of this class of vulnerabilities.