CVE-2026-100777 in Firefox
Summary
by MITRE • 09/29/2026
Use-after-free in the Graphics: Canvas2D component. This vulnerability was fixed in Firefox ESR 153.4, Firefox 157, Firefox ESR 115.42, and Firefox ESR 140.17.
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Analysis
by VulDB Data Team • 09/29/2026
The identified vulnerability represents a critical memory management error within the Graphics subsystem of Mozilla Firefox, specifically affecting the Canvas2D rendering component. This issue is classified as an use-after-free condition, which occurs when software continues to reference a block of memory after it has been deallocated or freed by the system. In the context of web browser engines like Gecko, this typically involves JavaScript objects that interact with HTML5 canvas elements. When a script modifies or removes a canvas element while other references to its underlying graphics resources remain active in the rendering pipeline, the application may attempt to access memory addresses that are no longer valid or have been repurposed for different data structures. This discrepancy between object lifecycle management and actual usage creates an unstable state within the browser process.
From a technical perspective, this flaw allows attackers who can trick a user into visiting a specially crafted web page to execute arbitrary code with the privileges of the victim. The Canvas2D API provides methods for drawing graphics via JavaScript, and improper handling of these resources during dynamic updates or removals leads to dangling pointers. An attacker could exploit this by crafting malicious HTML and JavaScript that triggers specific rendering operations followed immediately by resource deallocation, yet retaining references through event handlers or asynchronous callbacks. This exploitation vector is particularly dangerous because it bypasses many traditional sandboxing mechanisms if the renderer process gains sufficient access to system resources before being terminated.
The operational impact of such a vulnerability extends beyond simple application crashes, although denial-of-service remains a likely outcome for less sophisticated exploits. The primary risk lies in remote code execution, which can lead to full compromise of the user's machine. Attackers could install malware, steal sensitive data such as cookies and session tokens stored by the browser, or use the compromised system as part of a botnet. Given that Firefox is widely used across enterprise environments and personal devices, this vulnerability poses a significant threat to overall cybersecurity posture if left unpatched. The ability to execute code remotely makes it an attractive target for drive-by download attacks and targeted phishing campaigns where users are lured into interacting with malicious content.
Industry standards categorize this type of flaw under CWE-416, which defines use-after-free errors as a subset of improper resource validation or management vulnerabilities. In the context of the MITRE ATT&CK framework, exploitation techniques associated with such memory corruption bugs often fall under Tactic 7: Discovery and Tactic 8: Defense Evasion, specifically relating to process injection or API hooking once initial code execution is achieved. The vulnerability highlights the complexity of managing dynamic memory in high-performance graphics rendering engines where real-time updates are frequent and complex object relationships exist between DOM elements and their graphical representations.
Mitigation strategies primarily involve applying the software patches released by Mozilla for Firefox ESR 153.4, Firefox 157, Firefox ESR 115.42, and Firefox ESR 140.17. These updates contain code changes that ensure proper reference counting and lifecycle management of canvas resources, preventing access to freed memory blocks. Organizations should prioritize patching all affected versions immediately to close this attack vector. Additionally, implementing strict content security policies can help mitigate the impact by restricting the types of scripts allowed to interact with canvas elements, although such controls are secondary to timely software updates. Regular monitoring for new advisories and maintaining an up-to-date inventory of browser installations across endpoints is essential for minimizing exposure to memory corruption vulnerabilities in web browsers.