CVE-2026-117918 in Firefox
Summary
by MITRE • 10/27/2026
Use-after-free in the Graphics: Canvas2D component. This vulnerability was fixed in Firefox 159, Firefox ESR 115.44, and Firefox ESR 153.6.
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Analysis
by VulDB Data Team • 10/28/2026
The identified vulnerability represents a critical memory management error within the Mozilla Gecko rendering engine, specifically affecting the Canvas2D API implementation used for dynamic two-dimensional graphics rendering in web pages. This flaw is classified as an out-of-bounds write or use-after-free condition, which falls under CWE-416 (Use After Free) and potentially CWE-787 (Out-of-Bounds Write). The vulnerability arises when the internal memory allocator fails to properly manage the lifecycle of graphical objects during complex rendering operations. In a typical Canvas2D workflow, developers create drawing contexts that allocate buffers for pixel data or vector paths. When these resources are deallocated due to garbage collection or explicit removal from the DOM tree, the underlying C++ code must ensure that all references to those memory addresses are nullified or invalidated. However, in this specific instance, a race condition or logic error allows certain internal pointers to remain valid even after the associated memory has been returned to the system allocator for reuse by other processes or components.
From an operational perspective, this architectural flaw creates a severe security risk that extends beyond simple application crashes. While early exploitation attempts might result in denial-of-service conditions where the browser tab becomes unresponsive due to segmentation faults, sophisticated attackers can leverage the use-after-free state to achieve arbitrary code execution. By carefully crafting malicious JavaScript payloads and HTML structures, an attacker can control what data is written into the freed memory region before it is reallocated for a different purpose. This technique allows the injection of shellcode or the modification of function pointers within the browser process space. Since modern browsers operate with sandboxing mechanisms to limit damage from such exploits, this vulnerability remains particularly dangerous because successful exploitation could potentially allow an attacker to escape the browser's security container and execute code on the host operating system, thereby compromising user privacy and system integrity.
The technical context of this flaw is further contextualized by its alignment with MITRE ATT&CK techniques related to initial access and execution. Attackers typically distribute malicious web pages via phishing campaigns or compromised legitimate websites that contain obfuscated JavaScript designed to trigger the specific rendering conditions required to activate the bug. The exploit chain often involves multiple stages, including heap grooming to manipulate memory layout predictability, followed by the triggering of the Canvas2D operation that causes the premature deallocation and subsequent misuse of the pointer. This vulnerability highlights the complexity involved in maintaining secure state management within high-performance graphics libraries where performance optimizations sometimes conflict with strict safety checks. The presence of such bugs underscores the importance of rigorous fuzzing campaigns targeting rendering engines, as manual code review alone is often insufficient to catch subtle memory corruption issues that manifest only under specific timing or allocation patterns.
Mitigation for this vulnerability relies primarily on software updates provided by Mozilla. Users and system administrators must ensure that Firefox versions 159, Firefox Extended Support Release (ESR) version 115.44, and ESR version 153.6 are installed to patch the underlying memory management logic in the Canvas2D component. These releases include code changes that enforce stricter reference counting or add additional validation checks before allowing access to graphical resources. In environments where immediate patching is not feasible due to compatibility testing requirements, network-level security controls such as Web Application Firewalls (WAFs) can be configured to detect and block known exploit patterns associated with Canvas2D memory corruption attempts. Additionally, enabling browser sandboxing features like Site Isolation ensures that even if an attacker successfully exploits this vulnerability, the impact is contained within a single process, preventing access to sensitive data stored in other tabs or processes. Regular security audits of third-party JavaScript libraries used on corporate websites are also recommended to prevent accidental exposure of internal users to malicious content containing such exploit code.