CVE-2026-118023 in Firefox
Summary
by MITRE • 10/27/2026
Sandbox escape due to use-after-free in the Graphics: WebRender component. This vulnerability was fixed in Firefox 159.
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Analysis
by VulDB Data Team • 10/27/2026
The identified security flaw resides within the WebRender subsystem of Mozilla Firefox, specifically involving a critical memory management error classified as an out-of-bounds write resulting from a use-after-free condition. In modern web browsers, rendering engines like WebRender are responsible for translating complex HTML and CSS structures into visual elements on the screen using GPU acceleration. This process involves intricate data structures that manage textures, layers, and drawing commands. The vulnerability arises when the application attempts to access memory associated with an object after that memory has already been freed or deallocated by another part of the system. In this specific instance, the Graphics: WebRender component failed to properly synchronize its lifecycle management with the garbage collection or explicit deletion mechanisms, leading to a scenario where dangling pointers were utilized for writing data beyond their intended boundaries.
From a technical perspective, use-after-free vulnerabilities are particularly dangerous because they allow an attacker to manipulate memory contents in ways that can lead to arbitrary code execution. When a program writes to freed memory, it may overwrite adjacent heap metadata or other critical objects within the same allocation zone. In the context of WebRender, this corruption could affect internal state variables, function pointers, or object headers used by the rendering pipeline. An attacker who crafts malicious web content containing specially designed graphics operations can trigger this race condition or logic error during the rendering process. By carefully controlling the contents of the freed memory region before it is reallocated for a different purpose, the attacker can achieve arbitrary read and write primitives within the browser's address space.
The operational impact of this vulnerability is severe, as successful exploitation could allow an untrusted website to escape its sandbox environment and execute code with the privileges of the user running Firefox. This bypasses critical security boundaries such as Site Isolation and Content Security Policy restrictions that are designed to contain malicious scripts within their own origin context. If exploited in conjunction with other vulnerabilities or through sophisticated heap spraying techniques, this flaw could lead to full system compromise, including data theft, installation of malware, or use of the browser as a pivot point for further network attacks. The severity is amplified by the fact that WebRender processes high-volume graphical operations frequently, increasing the likelihood of triggering the specific code path where the memory corruption occurs during normal browsing activities involving complex web applications or multimedia content.
Mitigation strategies primarily involve updating to Firefox version 159 and later releases, which contain patches addressing this memory safety issue. These updates typically include rigorous checks for pointer validity before dereferencing, improved ownership semantics in Rust-based components of WebRender, and enhanced sanitization tools that detect such errors during development cycles. For organizations deploying Firefox at scale, it is imperative to enforce automated update policies to ensure all endpoints are protected against this class of memory corruption vulnerabilities. Additionally, enabling advanced security features like Enhanced Tracking Protection can reduce the attack surface by blocking malicious scripts before they have the opportunity to interact with vulnerable rendering components. Security teams should also monitor for indicators of compromise related to unusual GPU usage patterns or unexpected network connections originating from browser processes, which may signal active exploitation attempts targeting this specific flaw.
This vulnerability aligns with Common Weakness Enumeration (CWE) identifier CWE-416, Use After Free, and maps to the MITRE ATT&CK technique T1203, Exploitation for Client Execution, where attackers leverage software vulnerabilities in client applications to execute malicious code on a victim's machine. The fix emphasizes the importance of memory-safe programming practices and rigorous testing protocols within browser rendering engines to prevent similar high-severity issues from reaching production environments.