CVE-2026-109724 in Firefox
Summary
by MITRE • 10/13/2026
Use-after-free in the DOM: Core & HTML component. This vulnerability was fixed in Firefox 158 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, specifically affecting the core and HTML components of the browser engine. A use-after-free condition occurs when software continues to reference a pointer after the memory it points to has been reallocated or freed by another part of the system. In this specific instance, the flaw resides in how Firefox handles DOM elements during parsing or manipulation operations. When an attacker can trigger a sequence of events that causes a DOM node to be destroyed while references to that same node are still active within the JavaScript execution context or internal browser structures, the application retains access to memory that is no longer valid for its intended purpose. This scenario typically arises from complex interactions between HTML parsing routines and script execution engines where reference counting mechanisms fail to properly track object lifecycles under specific edge cases involving dynamic content modification.
From a technical perspective, this flaw allows an attacker who successfully exploits the vulnerability to execute arbitrary code with the privileges of the victim user. The immediate operational impact is severe because it bypasses standard browser sandboxing protections that rely on memory safety boundaries. By manipulating the freed memory block before it is reused by another process or data structure, a malicious actor can overwrite critical function pointers or object headers within the heap. This corruption enables control over program flow, leading to remote code execution without requiring any additional user interaction beyond visiting a crafted webpage. The vulnerability affects both Firefox 158 and Firefox ESR 153.5, indicating that it exists in recent stable releases as well as extended support versions used by enterprise environments where patching cycles may be slower or more rigidly controlled.
This type of memory corruption is classified under CWE-416, which defines use-after-free errors resulting from improper handling of deallocated memory regions. In the context of attack frameworks such as MITRE ATT&CK, this vulnerability facilitates initial access and execution capabilities often categorized under techniques involving browser exploitation or script processing vulnerabilities. The exploitability relies heavily on heap grooming techniques where an attacker carefully allocates and frees objects to control the layout of memory in a way that ensures their malicious payload is placed exactly into the freed slot. This precision allows for reliable code execution even against modern mitigations like ASLR, although DEP or NX bits may still prevent direct shellcode execution without additional information disclosure steps.
Mitigation strategies primarily involve applying the vendor-provided patches immediately to update the browser binaries and engine components. For enterprise deployments utilizing Firefox ESR 153.5, it is imperative that IT administrators verify patch compliance across all endpoints to ensure the underlying DOM parsing logic has been corrected to properly manage object lifecycles. Additionally, organizations should enforce strict content security policies to limit inline script execution and restrict access to potentially dangerous APIs that could be leveraged in conjunction with this memory corruption flaw. Monitoring for anomalous browser behavior or unusual network connections originating from local processes can also serve as a detection mechanism if exploitation attempts occur before patches are fully deployed across the infrastructure.