CVE-2026-109765 in Firefox
Summary
by MITRE • 10/13/2026
Race condition, use-after-free in the Graphics: Text 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 security flaw resides within the text rendering subsystem of Mozilla's Gecko engine, specifically affecting the Graphics: Text component. This area is critical for processing font data, glyph positioning, and layout calculations before content is rasterized to the screen. The vulnerability manifests as a race condition coupled with a use-after-free error, indicating that memory management operations are not properly synchronized when multiple threads or asynchronous processes interact with text objects during rendering pipelines. In complex web pages involving dynamic content updates, animations, or extensive typography processing, the browser may attempt to access memory associated with a text object after that memory has already been deallocated by another part of the system. This typically occurs due to insufficient locking mechanisms around shared data structures used for font metrics and glyph caches, allowing one thread to free resources while another is still referencing them.
From an operational perspective, this type of vulnerability poses significant risks beyond simple application crashes. While a use-after-free can lead to denial-of-service conditions through segmentation faults or memory corruption errors that terminate the browser process, it also presents opportunities for arbitrary code execution under specific exploitation scenarios. An attacker could potentially craft malicious web content designed to trigger these race conditions at precise moments during rendering, manipulating heap layouts to control what data is written into the freed memory region. If successful, this could allow an adversary to execute native code within the context of the browser process, leading to full system compromise depending on sandboxing effectiveness and other mitigating controls in place. The complexity lies in timing the exploit correctly against modern multi-threaded rendering engines where execution paths are highly parallelized.
Industry standards classify such flaws under CWE-362 for concurrent execution using shared resources with improper synchronization, which describes the race condition aspect of this vulnerability. Additionally, because it involves accessing memory after it has been freed, it falls squarely under CWE-416: Use After Free. In terms of offensive security frameworks like MITRE ATT&CK, this type of flaw is often leveraged during initial exploitation phases to achieve code execution or privilege escalation within the browser sandbox environment. The presence of these vulnerabilities highlights the inherent challenges in maintaining memory safety and thread consistency in large-scale software projects that handle untrusted input from web pages.
Mitigation for this issue has been implemented through updates to Firefox version 158 and Firefox Extended Support Release (ESR) version 153.5. These releases include patches that enforce stricter synchronization primitives around the text rendering components, ensuring that memory deallocation is properly serialized with access operations. Users are strongly advised to update their browsers immediately to these patched versions to eliminate the attack surface associated with this race condition and use-after-free vulnerability. For organizations relying on Firefox ESR for enterprise deployments, deploying version 153.5 or later via standard patch management systems is essential to maintain security posture against web-based exploitation attempts targeting rendering engine flaws.