CVE-2026-117931 in Firefox
Summary
by MITRE • 10/27/2026
Use-after-free in the DOM: Events 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 security flaw resides within the Document Object Model events subsystem of Mozilla Firefox, specifically classified as a use-after-free vulnerability. This type of memory corruption error occurs when program logic continues to reference a pointer after the memory it points to has been deallocated or freed by the system. In the context of browser engines like Gecko, which powers Firefox, this typically involves complex event handling mechanisms where objects representing DOM nodes or event listeners are dynamically created and destroyed during page rendering or user interaction. If an internal state is not properly synchronized with these lifecycle events, a reference to a previously valid object may persist in memory even after the underlying data structure has been reclaimed for reuse by other processes.
From a technical perspective, this vulnerability allows for arbitrary code execution under specific conditions. When the browser attempts to access the dangling pointer associated with the freed DOM event object, it reads from or writes to an invalid memory address. If an attacker can carefully control the contents of that reallocated memory region through crafted web content, they may be able to execute malicious instructions within the context of the user's browsing session. This mechanism is particularly dangerous because it bypasses many traditional sandboxing protections if the exploit chain successfully achieves code execution in a privileged process or escapes the browser's security boundaries entirely. The flaw highlights the complexity inherent in managing reference counts and object lifecycles in high-performance web rendering engines where asynchronous operations are common.
The operational impact of this vulnerability is severe, potentially leading to remote code execution on affected systems without any user interaction beyond visiting a maliciously crafted website. Attackers could leverage this weakness to install malware, steal sensitive data such as cookies or session tokens, or use the compromised browser as a pivot point for further network attacks. The severity is compounded by the fact that DOM manipulation and event handling are fundamental operations performed on nearly every modern web page, increasing the likelihood of encountering exploitable conditions in real-world scenarios. Users running affected versions of Firefox remain exposed to these risks until they update their software environment.
Mozilla addressed this issue in Firefox version 159 as well as in the Extended Support Release channels with updates to ESR 115.44 and ESR 153.6. These patches likely involve rigorous validation checks to ensure that object references are invalidated immediately upon deallocation or implementing safer memory management patterns such as smart pointers to prevent dangling references. To mitigate this risk, organizations should enforce strict update policies ensuring all endpoints run the patched versions of Firefox. Additionally, deploying browser isolation technologies and content security policies can provide additional layers of defense against exploitation attempts derived from similar vulnerabilities in other components.
This incident aligns with Common Weakness Enumeration identifier CWE-416 which describes use-after-free conditions as a critical class of memory safety errors. In the context of cyber attack frameworks such as MITRE ATT&CK, this vulnerability facilitates techniques related to initial access and execution, specifically those involving browser exploitation or script injection where memory corruption is leveraged to bypass security controls. Continuous monitoring for anomalous behavior in web content processing and keeping software dependencies current remain essential practices for maintaining robust cybersecurity postures against evolving threats targeting client-side applications.