CVE-2026-109726 in Firefox
Summary
by MITRE • 10/13/2026
Use-after-free in the SVG component. This vulnerability was fixed in Firefox 158, Firefox ESR 115.43, and Firefox ESR 153.5.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 10/13/2026
The identified vulnerability represents a critical memory management error classified as an out-of-bounds write resulting from a use-after-free condition within the Scalable Vector Graphics rendering engine of Mozilla Firefox browsers. This specific flaw occurs when the application continues to reference a block of memory that has already been deallocated by the system's garbage collector or explicit free operations. In the context of SVG processing, this typically involves complex DOM manipulations where elements are removed from the document tree while pending asynchronous tasks or event handlers still hold references to those objects. When the browser attempts to access properties or methods on these dangling pointers, it reads from or writes to memory locations that may have been reallocated for other purposes, leading to undefined behavior and potential exploitation scenarios.
From a technical perspective, this vulnerability aligns with Common Weakness Enumeration identifier CWE-416, which describes use-after-free errors where the program uses a pointer after freeing it. The operational impact of such a flaw is severe because modern browsers execute untrusted content from various websites daily. An attacker can craft a malicious webpage containing specially designed SVG code that triggers this race condition or state inconsistency during rendering. By carefully controlling the memory layout, an adversary could potentially achieve arbitrary read and write capabilities within the browser process space. This capability allows for sandbox escape, leading to remote code execution on the victim's machine without any user interaction beyond visiting the compromised site.
The vulnerability was addressed in Firefox version 158 as well as specific maintenance releases of the Extended Support Release channels, namely ESR 115.43 and ESR 153.5. These updates likely include patches that enforce stricter lifetime management for SVG DOM nodes or introduce additional checks to ensure that references are valid before dereferencing them. The fix ensures that once an object is marked for deletion, all active references are either nullified or the operation is deferred until it is safe to proceed. This prevents the browser from accessing freed memory and mitigates the risk of exploitation through standard web content.
In terms of threat intelligence frameworks, this vulnerability can be mapped to MITRE ATT&CK techniques related to initial access and execution via compromised applications. Specifically, it falls under the category of client-side attacks where attackers leverage software vulnerabilities in widely used tools like browsers to gain a foothold on target systems. The exploitation vector is primarily network-based, requiring no physical or local access by the attacker initially, making it a high-risk issue for organizations relying on web browsing for daily operations.
To mitigate this risk effectively, administrators and end-users must ensure that all instances of Firefox are updated to at least version 158 or the specified ESR patches mentioned above. For enterprise environments, deploying automated patch management systems can help maintain compliance with security baselines by ensuring timely application of browser updates. Additionally, implementing content security policies and restricting the execution of untrusted scripts on internal networks can reduce the attack surface presented to such vulnerabilities. Regular monitoring for new CVE disclosures related to core browsing components is also recommended to stay ahead of emerging threats in the web rendering ecosystem.