CVE-2026-92049 in Firefox
Summary
by MITRE • 09/15/2026
Use-after-free in the Widget: Win32 component. This vulnerability was fixed in Firefox 156 and Firefox ESR 153.3.
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Analysis
by VulDB Data Team • 09/15/2026
The identified vulnerability represents a critical memory management error within the Mozilla Gecko rendering engine, specifically affecting the Windows graphical user interface subsystem known as Widget: Win32. As an expert in software security, it is important to contextualize this flaw not merely as a coding mistake but as a fundamental violation of safe memory handling principles that can lead to severe system compromise. The vulnerability falls under the category of Use-After-Free (UAF), which corresponds directly to Common Weakness Enumeration identifier CWE-416. This class of vulnerabilities occurs when a program continues to use a pointer after it has been freed, leading to undefined behavior that attackers can exploit with high precision.
In the specific context of Firefox on Windows, the Widget: Win32 component is responsible for handling low-level user interface events such as mouse clicks, keyboard inputs, and window management tasks. When this component processes certain UI interactions or state changes, it may allocate memory to store temporary data structures related to widgets like buttons, menus, or input fields. If the application logic fails to properly manage the lifecycle of these objects, there exists a race condition or logical error where the underlying memory is deallocated while references to that memory are still retained by other parts of the browser process. An attacker who can trigger this specific sequence through crafted web content could cause the program to write to or read from freed heap memory.
The operational impact of exploiting a Use-After-Free vulnerability in a web browser is typically severe, often resulting in arbitrary code execution with the privileges of the current user. By carefully controlling the contents of the freed memory region and manipulating how subsequent allocations are handled, an attacker can achieve control over critical program pointers such as function return addresses or virtual table pointers. This allows for the execution of malicious shellcode within the browser process sandbox. While modern browsers employ various mitigation techniques including heap hardening, address space layout randomization, and sandboxing to limit the impact, a successful exploitation could potentially allow an attacker to escape the browser sandbox if additional vulnerabilities are chained together or if specific security boundaries are bypassed through this initial foothold.
This vulnerability was addressed in Firefox version 156 and Firefox Extended Support Release (ESR) version 153.3 by implementing stricter memory management protocols within the Widget: Win32 module. The fix likely involves ensuring that pointers to freed objects are immediately nullified, adding checks to prevent access after deallocation, or restructuring the object lifecycle to ensure no dangling references exist during critical UI operations. From a threat intelligence perspective, this aligns with ATT&CK technique T1059 which covers command and script interpreter execution, as UAF vulnerabilities in browsers have historically been primary vectors for drive-by download attacks where malicious scripts exploit browser flaws to execute payloads on the victim's machine without user interaction beyond visiting a compromised website.
To mitigate risks associated with this class of vulnerability, organizations should ensure that all endpoints are updated to at least Firefox 156 or ESR 153.3 immediately upon availability. For environments where immediate patching is not feasible due to compatibility testing requirements, network-level controls such as web filtering proxies can be configured to block access to known malicious domains that typically host exploit kits targeting browser vulnerabilities. Additionally, enabling strict content security policies and disabling JavaScript in untrusted zones for high-risk users can reduce the attack surface available to adversaries attempting to trigger this memory corruption flaw. Regular vulnerability scanning and patch management cycles are essential to maintain a secure posture against such memory safety issues which remain prevalent in complex software systems like web browsers.