CVE-2026-100797 in Firefox
Summary
by MITRE • 09/29/2026
Privilege escalation due to use-after-free in the Graphics: WebRender 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 security flaw resides within the Graphics WebRender component of Mozilla Firefox, representing a critical memory management error classified as an use-after-free vulnerability. This type of defect occurs when software continues to reference a pointer after the memory it points to has been reallocated or freed by the system. In the context of WebRender, which is responsible for compositing and rendering web content on the GPU, such a lapse in memory safety can lead to severe consequences if an attacker successfully exploits the condition. The vulnerability allows for privilege escalation, meaning that code executing within the browser's sandboxed environment could potentially break out into higher-privilege contexts or execute arbitrary commands with elevated rights depending on the specific execution path and system configuration.
From a technical perspective, use-after-free vulnerabilities are particularly dangerous because they can lead to undefined behavior in the application runtime. When the WebRender component accesses memory that has already been released, it may read stale data or write to memory locations controlled by an attacker. This scenario creates opportunities for heap corruption, which is often leveraged during exploit development to achieve arbitrary code execution. The Graphics subsystem operates at a low level with significant access to system resources, making any instability in this area potentially catastrophic for the integrity of the entire browser session and the underlying operating system.
The operational impact of this vulnerability extends beyond simple application crashes or denial-of-service scenarios. While memory corruption can certainly cause Firefox to become unstable or unresponsive, the primary concern is the potential for remote code execution through crafted web content. An attacker could design a malicious webpage that triggers the specific sequence leading to the use-after-free condition within WebRender. If successful, this would allow the injection of shellcode into the browser process memory space. Given that modern browsers run with restricted privileges by default, the ability to escalate privileges or escape the sandbox significantly increases the severity and potential damage of such an exploit in real-world attack scenarios involving targeted phishing campaigns or drive-by downloads.
Industry standards categorize this flaw under CWE-416, which defines use-after-free as a situation where a program uses memory after it has been freed, leading to unpredictable behavior. Furthermore, from the perspective of the MITRE ATT&CK framework, this vulnerability facilitates techniques associated with initial access and privilege escalation. Attackers typically rely on such vulnerabilities in widely used software like Firefox because they offer reliable entry points into user systems. The exploitation chain often involves crafting specific HTML or JavaScript payloads that interact with WebGL or CSS rendering engines to trigger the memory corruption within WebRender before the garbage collector can properly manage the allocated resources.
To mitigate this risk, users must ensure their browsers are updated to versions where the issue has been resolved. Specifically, deployment of Firefox ESR 153.4, Firefox 157, Firefox ESR 115.42, or Firefox ESR 140.17 is required to patch this vulnerability. These updates contain code changes that enforce stricter memory management protocols within the WebRender component, ensuring that pointers are invalidated immediately after deallocation and preventing access to freed memory regions. Organizations should prioritize updating their fleet of workstations running these affected versions to close the window of exposure. Additionally, enabling automatic update mechanisms can help maintain a consistent security posture by applying patches as soon as they become available from Mozilla.