CVE-2026-117967 in Firefox
Summary
by MITRE • 10/27/2026
Mitigation bypass in the DOM: Security component. This vulnerability was fixed in Firefox 159 and Firefox ESR 153.6.
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Analysis
by VulDB Data Team • 10/27/2026
The identified vulnerability represents a critical failure within the Document Object Model security components of Mozilla Firefox, specifically affecting versions prior to 159 and Firefox Extended Support Release 153.6. This flaw constitutes a mitigation bypass, indicating that existing browser-level protections designed to restrict or sanitize certain DOM operations were circumvented by crafted input. In modern web browsers, the DOM serves as the primary interface for JavaScript to interact with webpage content, making it a frequent target for exploitation attempts aimed at achieving cross-site scripting or unauthorized data access. The security components responsible for validating and sanitizing these interactions failed to correctly enforce boundaries between trusted script context and untrusted user input, allowing malicious actors to execute code that was previously blocked by standard sandboxing mechanisms.
From a technical perspective, this vulnerability likely stems from an inconsistency in how the browser parses or processes specific DOM APIs when subjected to edge-case inputs designed to trigger logic errors within the security filters. Such bypasses often occur when developers rely on heuristic checks rather than strict allow-lists for dangerous methods or properties. By exploiting these gaps, an attacker can manipulate the execution environment of a victim user's session. This could lead to scenarios where malicious scripts are injected into otherwise secure pages, enabling the theft of sensitive information such as authentication tokens, cookies, or personal data stored in local storage. The success of this attack relies on convincing a user to visit a specially crafted webpage that triggers the flawed DOM processing logic within their browser instance.
The operational impact of this vulnerability is significant due to its potential for remote code execution and session hijacking. If an attacker successfully exploits this mitigation bypass, they can achieve arbitrary script execution in the context of the victim's current website origin. This effectively breaks the same-origin policy protections that are fundamental to web security. The consequences include complete compromise of user privacy on affected sites, potential defacement of websites if the vulnerability allows for DOM manipulation beyond data theft, and further propagation of malware through drive-by download techniques facilitated by the elevated privileges gained within the browser sandbox. Users relying on older versions of Firefox or its ESR variant remain exposed to these risks until they upgrade to a patched version that corrects the underlying logic errors in the security component.
To mitigate this risk, immediate action is required for all systems running vulnerable versions of Mozilla Firefox and Firefox Extended Support Release 153.x. Administrators should enforce automatic updates or manually deploy patches to ensure users are operating on Firefox version 159 or later, as well as ESR version 153.6 or newer. These releases contain the necessary code changes that close the logic gaps exploited by this mitigation bypass. In environments where immediate patching is not feasible due to compatibility concerns with legacy applications, network-level filtering solutions should be configured to block access to known malicious domains and restrict execution of untrusted scripts via Content Security Policy headers enforced at the proxy level. Additionally, users should exercise caution when interacting with unfamiliar websites or clicking on links from untrusted sources until their browser software is fully updated.
This vulnerability aligns with Common Weakness Enumeration categories such as CWE-79 for Improper Neutralization of Input During Web Page Generation and CWE-20 for Improper Input Validation. It also maps to MITRE ATT&CK techniques related to Client-side Execution, specifically T1059 which covers command and script interpretation through browser-based vectors. Understanding these classifications helps security teams prioritize remediation efforts based on industry-standard risk frameworks. The resolution underscores the importance of rigorous testing in browser development cycles, particularly for components that handle untrusted input within complex rendering engines like Gecko. Continuous monitoring for similar patterns in future updates will help maintain robust defenses against evolving web-based attack vectors.