CVE-2026-100789 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 Canvas2D component of Mozilla Firefox browsers, specifically classified as an use-after-free condition. This type of flaw 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 rendering engines like those used in Firefox, this typically involves complex interactions between JavaScript execution and native C++ code responsible for drawing graphics on HTML5 canvas elements. When an object representing graphical data is destroyed while still being referenced by another part of the application, such as a pending paint operation or event handler, the program may attempt to read from or write to that invalid memory address. This scenario creates a window where arbitrary code execution can potentially be achieved if an attacker can control the contents of the freed memory region and trick the browser into executing it.
From a technical perspective, Canvas2D vulnerabilities often arise due to race conditions or improper lifecycle management of graphical resources. An attacker could craft a malicious webpage containing specific JavaScript commands that trigger rapid creation and destruction of canvas contexts or image data objects. By carefully timing these operations, the attacker might cause the browser to retain pointers to memory that has already been returned to the heap allocator. If subsequent allocations reuse this freed memory for different purposes controlled by the attacker, such as storing shellcode or ROP gadgets, the dangling pointer will inadvertently point to malicious content rather than legitimate application data. This mechanism allows for out-of-bounds reads which can lead to information disclosure of sensitive browser internals, or more severely, out-of-bounds writes that facilitate arbitrary code execution with the privileges of the user running the browser.
The operational impact of this vulnerability is severe due to its potential for remote code execution through standard web browsing activities. Users visiting a compromised website could trigger the exploit without any additional interaction beyond loading the page, depending on how the Canvas2D operations are invoked. This aligns with common attack vectors found in modern web exploitation where browser-based attacks bypass traditional perimeter defenses by leveraging trusted applications like browsers to establish footholds within enterprise networks or personal devices. The vulnerability affects multiple versions of Firefox including ESR branches 153.4, 157, 115.42, and 140.17, indicating a systemic issue in the rendering engine's handling of canvas resources across different release tracks rather than an isolated incident in a single version line.
In terms of industry standard classifications, this vulnerability maps directly to CWE-416 Use After Free, which describes situations where pointers are used after they have been freed leading to unpredictable behavior and potential security breaches. Furthermore, from the perspective of the MITRE ATT&CK framework, such vulnerabilities often support techniques related to Initial Access via Spearphishing Attachment or Drive-by Compromise, as well as Execution through Browser-based attacks like Command and Scripting Interpreter abuse within a sandboxed environment that may be escaped due to this memory corruption flaw. The exploitation chain typically involves bypassing browser security mitigations such as ASLR and DEP by achieving arbitrary read/write primitives via the use-after-free condition.
Mitigation strategies primarily involve applying the provided software updates immediately, as patches for Firefox ESR 153.4, Firefox 157, Firefox ESR 115.42, and Firefox ESR 140.17 have been released to address these memory management errors. These fixes likely include rigorous checks on pointer validity before dereferencing, improved reference counting mechanisms for canvas objects, or enhanced sandboxing boundaries that limit the impact of any successful exploitation attempt. Organizations should ensure automated patch management processes are in place to deploy these updates across all endpoints running affected browser versions. Additionally, implementing strict content security policies and disabling JavaScript execution for untrusted domains can reduce the attack surface by preventing malicious scripts from interacting with canvas elements altogether. Security teams should also monitor for indicators of compromise associated with known exploit kits targeting this specific vulnerability class until full patch compliance is achieved.