CVE-2026-117943 in Firefox
Summary
by MITRE • 10/27/2026
Use-after-free in the DOM: Core & HTML 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 within the Document Object Model core and HTML components of Mozilla Firefox browsers. Specifically classified as an use-after-free condition, this flaw occurs when the application continues to reference a block of memory after it has been deallocated or freed by the system. In the context of web browser engines, such errors typically arise during complex interactions between JavaScript execution and DOM manipulation routines where object lifecycles are not strictly synchronized with garbage collection mechanisms. When an attacker can trigger this specific sequence through crafted HTML or script content, they gain the ability to access memory that is no longer valid for the intended operation, leading to undefined behavior within the browser process.
From a technical perspective, use-after-free vulnerabilities in browser components are particularly dangerous because they allow attackers to manipulate how the application interacts with system memory. By carefully controlling the allocation and deallocation of objects through malicious web content, an attacker can often overwrite freed memory regions with controlled data structures. This manipulation enables arbitrary code execution within the context of the compromised process. The vulnerability affects the core rendering engine responsible for parsing HTML elements and managing their lifecycle in the DOM tree. When these internal structures are corrupted due to premature access or improper cleanup routines, it creates a pathway for exploit developers to achieve remote code execution on the victim's machine without any user interaction beyond visiting a malicious webpage.
The operational impact of this vulnerability is severe, as it compromises the integrity and confidentiality of the entire browsing session. Successful exploitation allows an attacker to execute arbitrary commands with the privileges of the affected application. This can lead to full system compromise if the browser runs with elevated permissions or if subsequent exploits leverage other vulnerabilities in the operating system kernel or installed plugins. The risk is amplified by the widespread usage of Firefox across enterprise and personal environments, making it a high-value target for cybercriminals seeking initial access points into corporate networks or individual devices. Data exfiltration, installation of persistent malware, and lateral movement within internal networks are all potential outcomes following successful exploitation of this flaw.
This vulnerability aligns with Common Weakness Enumeration identifier CWE-416, which defines use-after-free errors as a distinct category of memory corruption bugs. In the context of cyber attack frameworks such as MITRE ATT&CK, this type of exploit falls under techniques related to initial access and execution via browser-based attacks. The specific component affected involves DOM core and HTML parsing logic, indicating that the flaw is triggered during standard web page rendering processes rather than through specialized plugins or extensions. This makes the vulnerability broadly applicable across various types of malicious websites designed specifically to target modern browsers.
Mitigation strategies primarily rely on applying the software updates released by Mozilla Corporation. The issue was resolved in Firefox version 159, as well as in extended support release versions 115.44 and 153.6. Organizations should prioritize patching all endpoints running affected browser versions to eliminate this attack vector. Additionally, implementing strict content security policies can help mitigate the impact of similar vulnerabilities by restricting how scripts interact with DOM elements. Enabling automatic updates ensures that users receive these critical fixes promptly without requiring manual intervention. Security teams should also monitor for indicators of compromise associated with exploitation attempts targeting known use-after-free flaws in browser engines to detect potential breaches early.