CVE-2026-117938 in Firefox
Summary
by MITRE • 10/27/2026
Use-after-free in the Layout component. This vulnerability was fixed in Firefox 159, Firefox ESR 115.44, and Firefox ESR 153.6.
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Analysis
by VulDB Data Team • 10/27/2026
The identified vulnerability represents a critical memory management error classified as an out-of-bounds write due to use-after-free conditions within the Layout component of Mozilla Firefox browsers. This specific flaw arises when the application continues to reference a block of memory that has already been deallocated by the system, leading to undefined behavior during rendering operations. In complex web environments where dynamic content is frequently updated or removed from the Document Object Model, the browser's layout engine may inadvertently retain pointers to freed objects if proper synchronization and nullification checks are not enforced before subsequent access attempts. This scenario typically occurs when asynchronous events trigger garbage collection while a pending layout calculation still holds references to those same memory regions, creating a race condition that compromises data integrity within the rendering pipeline.
From a technical perspective, this vulnerability aligns with Common Weakness Enumeration identifier CWE-416, which describes use-after-free errors resulting in out-of-bounds writes or reads. The exploitation of such flaws allows attackers to manipulate heap metadata or overwrite adjacent memory structures, potentially leading to arbitrary code execution if the attacker can control the data written into the freed memory space before it is reallocated for malicious purposes. This type of vulnerability falls under the MITRE ATT&CK technique T1203, which covers exploitation for client-side execution, specifically targeting browser-based attack vectors where users are tricked into visiting a specially crafted webpage that triggers the malformed layout calculations. The severity is heightened by the fact that modern browsers employ sophisticated sandboxing mechanisms, but successful exploitation of memory corruption bugs can sometimes allow escape from these sandboxes depending on the specific context and available exploit primitives.
The operational impact of this vulnerability extends beyond simple application crashes or denial-of-service scenarios to include significant security risks involving remote code execution. An attacker could craft a malicious webpage that exploits the timing window between object deallocation and subsequent access within the layout engine, thereby gaining unauthorized control over the browser process. This compromise can lead to data exfiltration, installation of persistent malware, or further lateral movement within a network if the user is operating with elevated privileges. Given the widespread adoption of Firefox across enterprise environments utilizing Extended Support Releases, the potential for large-scale impact remains high unless immediate remediation measures are implemented by end-users and system administrators alike.
Mitigation strategies primarily involve ensuring that all affected browser versions are updated to their latest secure releases as soon as possible. Mozilla has addressed this issue in Firefox version 159, as well as in specific Extended Support Release branches including ESR 115.44 and ESR 153.6. Organizations should prioritize patching these endpoints through automated update mechanisms or centralized deployment tools to minimize the window of exposure. Additionally, implementing strict content security policies can help mitigate some risks by restricting the types of scripts that execute within browser contexts, although this does not directly prevent memory corruption vulnerabilities inherent in the rendering engine itself. Regular vulnerability scanning and monitoring for indicators of compromise related to heap spraying techniques are also recommended as part of a defense-in-depth strategy against such sophisticated client-side attacks.