CVE-2026-74939 in Firefox
Summary
by MITRE • 08/18/2026
Privilege escalation in the DOM: Navigation component. This vulnerability was fixed in Firefox 154, Firefox ESR 115.39, Firefox ESR 140.14, and Firefox ESR 153.1.
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Analysis
by VulDB Data Team • 08/19/2026
The identified vulnerability represents a critical flaw within the Document Object Model navigation component of Mozilla Firefox browsers, specifically classified as a privilege escalation issue. This type of defect typically arises when the browser fails to correctly enforce security boundaries between different execution contexts or origins during DOM manipulation and navigation events. In standard web architecture, the same-origin policy is designed to restrict how documents or scripts loaded from one origin can interact with resources from another origin. However, in this specific instance, the internal logic governing how the navigation component processes state changes allows an attacker to bypass these restrictions. By crafting a malicious webpage that exploits the race conditions or improper validation within the DOM API calls related to history and location objects, it is possible for unauthorized scripts to gain elevated privileges beyond what their origin should permit. This effectively breaks the isolation model that protects users from cross-site scripting attacks and data theft, allowing code running in a less privileged context to access sensitive information or perform actions reserved for higher-privileged contexts such as the browser chrome or other tabs.
From a technical perspective, this vulnerability likely stems from insufficient checks on the caller's origin when handling navigation-related DOM methods. When a script attempts to modify the URL or navigate through history entries, the browser must verify that the action is permitted by security policies. The flaw suggests that these verification steps were either skipped or bypassed under certain conditions, possibly involving complex interactions between asynchronous JavaScript execution and synchronous UI updates. This misalignment allows an attacker to manipulate the DOM in ways that expose internal browser states or inject malicious content into trusted contexts. Such behavior aligns with common patterns found in CWE-269 Improper Privilege Management and CWE-749 Exposed Dangerous Method, where sensitive methods are accessible without adequate authorization checks. The exploitation of this flaw could lead to severe consequences including session hijacking, credential theft, or the ability to phish users by spoofing legitimate website interfaces within a trusted frame context.
The operational impact of this vulnerability is significant because it undermines the fundamental trust model of web browsers. Users rely on Firefox and its Extended Support Release variants to isolate malicious content from their personal data and browsing sessions. A successful exploit could allow an attacker to read cookies, local storage, or other sensitive data belonging to a different origin that was previously inaccessible. Furthermore, if the privilege escalation allows interaction with browser chrome elements, it could facilitate more advanced attacks such as keylogging or UI redressing where the user is deceived into entering credentials on a fake login page that appears legitimate due to its integration within the trusted browsing context. This affects not only individual users but also enterprise environments relying on Firefox ESR versions for stable and secure operations across large deployments.
To mitigate this risk, it is imperative to update all affected installations immediately. The vulnerability has been addressed in Firefox version 154 as well as specific maintenance releases of the Extended Support Release channels including Firefox ESR 115.39, Firefox ESR 140.14, and Firefox ESR 153.1. Organizations should enforce automated patch management policies to ensure that these updates are deployed across all endpoints without delay. Additionally, implementing strict Content Security Policy headers can help limit the impact of any residual vulnerabilities by restricting script execution sources and preventing unauthorized DOM manipulations. Monitoring for unusual navigation patterns or unexpected access to sensitive APIs may also aid in detecting potential exploitation attempts before significant damage occurs. Maintaining up-to-date software is the most effective defense against such privilege escalation flaws, as they are often targeted specifically at older versions where known attack vectors remain unpatched.