CVE-2026-117997 in Firefox
Summary
by MITRE • 10/27/2026
Sandbox escape due to use-after-free in the Widget component. This vulnerability was fixed in Firefox 159 and Firefox ESR 153.6.
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Analysis
by VulDB Data Team • 10/27/2026
The identified security flaw represents a critical memory corruption issue within the Mozilla Gecko rendering engine, specifically located in the Widget subsystem which handles user interface elements such as pop-ups, context menus, and native window interactions. This vulnerability is classified under CWE-416, Use After Free, indicating that the application attempts to access memory after it has been freed or deallocated by the system. In complex software architectures like Firefox, the widget component manages a significant amount of state regarding user interface events and platform-specific integrations. When an object representing a UI element is destroyed, its underlying memory should be invalidated immediately. However, due to this flaw, certain references to that object persist in memory pointers or data structures even after the allocation has been reclaimed by the operating system's memory manager.
From a technical perspective, the exploitation of this use-after-free condition allows an attacker who can trigger specific widget-related events through malicious web content to manipulate the contents of the freed memory region. Since modern browsers employ various heap hardening techniques such as ASLR and stack canaries, simply crashing the browser is often insufficient for successful exploitation. Instead, attackers typically engage in a technique known as heap spraying or object reuse, where they allocate new objects into the same memory space previously occupied by the vulnerable widget component. By carefully controlling what data is written to this reused memory block, an attacker can achieve arbitrary code execution within the context of the browser process. This effectively constitutes a sandbox escape, allowing malicious scripts running in a restricted web environment to break out and execute commands with higher privileges on the host operating system.
The operational impact of this vulnerability is severe because it compromises the fundamental isolation model that protects users from untrusted internet content. If successfully exploited, an attacker could install malware, steal sensitive data such as passwords or session cookies, or use the compromised browser instance to pivot into other parts of a user's network infrastructure. The risk is particularly acute for enterprise environments where Firefox ESR versions are deployed across many endpoints, potentially exposing large numbers of systems if updates are delayed. Although the vulnerability was addressed in Firefox version 159 and Firefox Extended Support Release (ESR) version 153.6, any system running older versions remains vulnerable to remote code execution attacks triggered by visiting specially crafted web pages or interacting with malicious extensions that manipulate widget states.
Mitigation strategies primarily involve ensuring that all instances of the browser are updated to the patched versions mentioned above. For organizations managing large fleets of devices, automated patch management systems should be configured to prioritize these updates due to the high severity and active exploitation potential associated with memory corruption vulnerabilities in browsers. Additionally, security teams can employ application control policies or exploit prevention technologies such as Microsoft EMET on Windows or similar sandboxing mechanisms that restrict how browser processes interact with system resources. While user education regarding suspicious links remains relevant, technical controls are essential because this vulnerability relies on complex heap manipulation techniques that are difficult for end-users to detect through behavioral analysis alone. The fix likely involved adding proper null checks and ensuring that all references to the widget object are cleared upon destruction, thereby preventing any subsequent access attempts from reaching freed memory regions.