CVE-2026-117866 in Firefox
Summary
by MITRE • 10/27/2026
Privilege escalation due to 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 security flaw resides within the Graphics subsystem of Mozilla Firefox, specifically affecting the Canvas2D rendering engine which is responsible for handling two-dimensional drawing operations on web pages via HTML5 canvas elements. This vulnerability manifests as a use-after-free error, a critical memory management defect where the application continues to reference a block of memory after it has been deallocated or freed by the system. In the context of browser-based attacks, such flaws are particularly dangerous because they allow an attacker who can trick a user into visiting a specially crafted webpage to manipulate how the browser handles internal data structures related to canvas rendering operations. The root cause typically involves a race condition or improper lifecycle management where pointers to graphics resources remain valid in code paths even after those resources have been released, leading to undefined behavior when subsequent drawing commands attempt to access these stale memory addresses.
From an operational perspective, this vulnerability poses a severe risk of privilege escalation within the browser process context. When exploited successfully, use-after-free conditions can lead to arbitrary read and write capabilities across the application's memory space. This capability enables attackers to bypass security mitigations such as sandboxing mechanisms that are designed to isolate web content from the rest of the system. By carefully crafting malicious JavaScript code or WebGL interactions that trigger the specific sequence leading to the dangling pointer dereference, an attacker can corrupt internal data structures, overwrite function pointers, or hijack control flow execution paths. This ultimately allows for the execution of arbitrary code with the same privileges as the browser process itself, which may have broader access rights than a standard web page context would normally permit under strict sandboxing policies.
The technical implications align closely with CWE-416, Use After Free, and are frequently associated with ATT&CK technique T1203, Exploitation for Client Execution, as well as potential lateral movement vectors if the browser process has elevated permissions or access to sensitive local resources. The vulnerability highlights the complexity of managing memory in high-performance graphics APIs where rapid allocation and deallocation cycles are common during rendering updates. Attackers often leverage such flaws to establish a foothold on an end-user machine, potentially leading further into post-exploitation activities including data exfiltration, credential theft from browser storage, or installation of persistent malware components if the sandbox boundaries can be fully breached.
To mitigate this risk, it is imperative that all users and organizations deploy the latest available updates for Mozilla Firefox immediately upon release. The vulnerability was addressed in Firefox version 159 as well as specific extended support releases including Firefox ESR 115.44 and Firefox ESR 153.6. These patches include code changes to ensure proper memory lifecycle management within the Canvas2D component, preventing access to freed memory blocks during rendering operations. Organizations relying on enterprise deployments should verify that their automated patching systems are configured to prioritize these specific version updates. Additionally, implementing strict content security policies and restricting execution of untrusted scripts can reduce the attack surface by limiting the ability of malicious web pages to trigger complex graphics interactions that might exploit such low-level memory errors. Regular auditing of browser configurations and ensuring timely application of vendor-supplied fixes remain essential practices for maintaining robust defense-in-depth strategies against zero-day style exploitation attempts targeting rendering engines.