CVE-2026-109728 in Firefox
Summary
by MITRE • 10/13/2026
Use-after-free in the DOM: Animation 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 use-after-free condition within the Document Object Model animation subsystem of Mozilla Firefox browsers. A use-after-free error occurs when software continues to reference memory that has already been deallocated by the system. In this specific context, the flaw resides in how the browser handles animations associated with DOM elements. When an element is removed from the document tree or its state changes such that it should no longer be animated, the underlying memory allocated for tracking and executing these animation states may be freed prematurely. However, if internal references to this memory block are not properly nullified or updated before the deallocation occurs, subsequent operations attempting to access or modify the animation data will interact with invalid pointers. This scenario creates a window of opportunity where an attacker can manipulate the state of the browser to trigger these dangling pointer accesses during routine rendering or event handling processes.
From a technical perspective, this flaw exploits the complex lifecycle management required for asynchronous DOM updates and CSS animations. The vulnerability likely stems from a race condition or logic error in the garbage collection mechanisms tied to animation frames. When an attacker constructs a malicious webpage containing specially crafted JavaScript that manipulates DOM elements while triggering rapid style changes or animation sequences, they can force the browser into a state where it attempts to read or write to memory locations that have already been returned to the operating system for reuse. This misalignment between object lifetime and reference validity is particularly dangerous because modern browsers employ sophisticated sandboxing techniques designed to contain damage from exploits. However, use-after-free vulnerabilities are historically among the most potent attack vectors in browser security because they allow attackers to achieve arbitrary read or write capabilities within the process memory space of the browser engine.
The operational impact of this vulnerability is severe and directly threatens user confidentiality and system integrity. An attacker who successfully exploits this flaw can execute arbitrary code with the privileges of the victim, effectively taking control of the web application context in which the browser operates. This capability allows for a wide range of malicious activities including stealing sensitive cookies, session tokens, or authentication credentials stored within the browser memory. Furthermore, it enables data exfiltration from other tabs if same-origin policies are bypassed through heap spraying techniques often paired with use-after-free exploits. In worst-case scenarios, this vulnerability can serve as an entry point for drive-by download attacks where malicious payloads are silently downloaded and executed on the victim's machine without any user interaction beyond visiting a compromised website.
To mitigate the risks associated with this class of vulnerabilities, immediate action is required to ensure all instances of Firefox are updated to version 158 or later, including Extended Support Release versions 115.43 and 153.5 which contain specific patches for this issue. These updates include fixes that properly manage memory deallocation sequences and add safeguards against accessing freed animation objects. Beyond software patching, organizations should enforce strict content security policies to limit the execution of inline scripts and restrict access to potentially dangerous APIs used in DOM manipulation attacks. Additionally, enabling automatic update mechanisms ensures that users receive critical security patches promptly as they are released by Mozilla. Security teams should also monitor for indicators of compromise related to browser memory corruption events which may signal attempted exploitation attempts against unpatched systems within their network perimeter.
This vulnerability aligns with Common Weakness Enumeration identifier CWE-416, which describes use-after-free conditions resulting from improper management of dynamic memory allocation and deallocation. In the context of the MITRE ATT&CK framework for enterprise security, this flaw facilitates techniques associated with initial access via drive-by compromise and subsequent execution through browser-based code injection. The exploitation path typically involves crafting a malicious webpage that triggers the specific DOM manipulation sequence leading to the dangling pointer dereference. Defenders should prioritize patching strategies focused on endpoint protection platforms capable of detecting anomalous memory access patterns indicative of heap corruption exploits. Regular vulnerability assessments targeting web browsers and their rendering engines remain essential for maintaining resilience against such high-severity flaws in modern internet infrastructure.