CVE-2026-109735 in Firefox
Summary
by MITRE • 10/13/2026
Use-after-free in the DOM: Animation component. This vulnerability was fixed in Firefox 158.
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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 implementation of Mozilla Firefox, specifically affecting the animation subsystem. As a use-after-free flaw, this defect occurs when the application attempts to access or manipulate a block of memory that has already been deallocated by the system. In the context of browser engines like Gecko, which powers Firefox, the DOM serves as the structural backbone for web pages, and animations are frequently managed through complex object lifecycles involving JavaScript event handlers, CSS transitions, and compositor threads. When an animation component is removed or destroyed while references to it remain active in other parts of the rendering pipeline, the memory pointer becomes dangling. If subsequent operations attempt to read from or write to this invalid address, the result is undefined behavior that can lead to application crashes or more severe security compromises.
From a technical perspective, this flaw typically arises due to improper synchronization between garbage collection mechanisms and asynchronous animation updates. Modern browsers rely heavily on reference counting and mark-and-sweep algorithms to manage memory for dynamic web content. If an object representing an active animation is freed prematurely while still being referenced by a pending task or a callback function, the pointer retains its value but points to invalid data. This scenario creates a window of opportunity where an attacker who can control the state of DOM elements and trigger specific timing conditions might exploit this race condition. The vulnerability falls under the Common Weakness Enumeration category CWE-416, which classifies use-after-free errors as high-risk issues due their potential for arbitrary code execution.
The operational impact of such a vulnerability is severe because it can be triggered by visiting a maliciously crafted webpage or interacting with compromised web content. An attacker could potentially leverage this flaw to achieve remote code execution on the victim's machine. By carefully crafting memory contents after the free operation, an adversary might overwrite function pointers or vtable entries within adjacent heap allocations. This technique allows for control over the program counter, enabling the injection and execution of arbitrary shellcode. Furthermore, even if full code execution is mitigated by modern browser security features such as sandboxing and data execution prevention, the vulnerability can still be used to cause denial-of-service conditions through consistent application crashes or memory corruption that destabilizes the entire browsing session.
Mitigation strategies for this class of vulnerabilities primarily involve rigorous adherence to safe coding practices within the engine's source code. Developers must ensure that all references to animation objects are nullified immediately upon deallocation and implement robust checks before any access is performed on potentially freed pointers. Additionally, employing memory safety tools such as AddressSanitizer during development can help detect these issues early in the lifecycle. For end-users, the primary defense remains timely software updates. Mozilla addressed this specific issue by releasing Firefox version 158, which includes patches to correct the object lifetime management within the animation component. Users are strongly advised to update their browsers immediately to close this attack vector and protect against potential exploitation attempts targeting older versions of the software.
This incident highlights the ongoing challenges in maintaining memory safety in complex web rendering engines that handle high-frequency updates and asynchronous operations. The vulnerability aligns with tactics observed in advanced persistent threats, where browser exploits are used as initial access vectors for broader network intrusions. According to the MITRE ATT&CK framework, such vulnerabilities facilitate techniques related to client-side exploitation and potentially privilege escalation if sandbox boundaries are breached. Continuous monitoring of security advisories from software vendors is essential for maintaining a secure browsing environment against these sophisticated memory corruption attacks.