CVE-2026-109738 in Firefox
Summary
by MITRE • 10/13/2026
Use-after-free in the Audio/Video: Playback component. This vulnerability was fixed in Firefox 158 and Firefox ESR 153.5.
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Analysis
by VulDB Data Team • 10/14/2026
The identified vulnerability represents a critical memory management error classified as an out-of-bounds write, specifically manifesting through a use-after-free condition within the Audio/Video playback subsystem of Mozilla Firefox. This class of defect occurs when the application attempts to access or manipulate a block of memory that has already been deallocated by the system's garbage collector or explicit free operations. In the context of browser-based media processing, such errors are particularly dangerous because they can be triggered through standard web content interactions involving HTML5 audio and video elements. The flaw likely stems from improper handling of object lifecycles during complex playback scenarios, where references to memory regions may persist after those regions have been released back to the heap for reuse by other processes or data structures.
From a technical perspective, this vulnerability falls under CWE-416, which defines use-after-free as a condition resulting in undefined behavior that can lead to crashes, data corruption, or arbitrary code execution. When an attacker successfully exploits this flaw, they can craft malicious web content containing specially designed media files or JavaScript sequences that force the browser to free specific memory blocks while retaining active pointers to them. By subsequently triggering operations on these dangling pointers, the attacker gains control over how the freed memory is interpreted and modified. This capability allows for precise manipulation of heap structures, potentially leading to arbitrary read/write primitives within the browser process context.
The operational impact of this vulnerability extends beyond simple application instability or denial-of-service conditions. While a crash may occur if the system detects invalid access patterns, sophisticated exploitation techniques can bypass these protections to achieve remote code execution on the victim's machine. This aligns with MITRE ATT&CK technique T1203, which covers exploitation for client-side attacks, and specifically relates to browser-based exploits that leverage memory corruption vulnerabilities to establish a foothold within the user environment. Given that Firefox is widely used across enterprise and personal environments, successful exploitation could allow an attacker to install malware, steal sensitive credentials stored in the browser, or pivot further into internal networks if the victim has access to restricted resources.
To mitigate this risk, users must ensure they are running Mozilla Firefox version 158 or later, as well as any supported Extended Support Release (ESR) versions including 153.5 and beyond. These updates contain specific patches that correct the memory management logic within the playback component, ensuring that object references are properly invalidated upon deallocation. Organizations should enforce automated update policies to guarantee rapid deployment of these security fixes across all endpoints. Additionally, implementing browser hardening techniques such as disabling unnecessary plugins or restricting script execution in untrusted zones can reduce the attack surface available for triggering this vulnerability until full patching is achieved.