CVE-2026-74971 in Firefox
Summary
by MITRE • 08/18/2026
Information disclosure in the DOM: UI Events & Focus Handling component. This vulnerability was fixed in Firefox 154, Firefox ESR 140.14, and Firefox ESR 153.1.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 08/18/2026
The identified vulnerability resides within the Document Object Model's handling of user interface events and focus management mechanisms in Mozilla Firefox browsers. This specific flaw allows for unintended information disclosure by exposing internal state or data that should remain isolated from external scripts or malicious actors. The issue stems from how the browser processes focus-related events, potentially leaking sensitive context such as active tab identities, window states, or other DOM properties to untrusted content under certain conditions. Such exposure can be leveraged by attackers to fingerprint user environments or gather intelligence for further exploitation attempts against web applications hosted within the affected browsing session.
From a technical perspective, this vulnerability is classified under CWE-200 as an Information Exposure Vulnerability, specifically relating to improper restriction of information access rights. The root cause lies in the event propagation and focus handling logic where sensitive attributes or states are inadvertently made accessible through standard DOM APIs when they should be restricted by same-origin policies or other security boundaries. This misconfiguration enables cross-context data leakage, which violates fundamental web isolation principles designed to prevent malicious scripts from accessing resources belonging to different origins. The flaw highlights the complexity of maintaining strict separation between privileged browser internals and untrusted webpage content during dynamic UI interactions.
The operational impact of this vulnerability is primarily centered around reconnaissance and profiling activities by threat actors. By exploiting the focus handling discrepancy, an attacker can potentially determine which tabs are active, identify specific user interfaces being interacted with, or infer behavioral patterns based on event timing and state changes. While not directly leading to remote code execution in isolation, such information disclosure significantly lowers the barrier for subsequent attacks including session hijacking, targeted phishing, or more sophisticated cross-site scripting campaigns that rely on precise environmental knowledge. The risk is particularly acute when users interact with sensitive applications like banking portals or enterprise dashboards where contextual awareness can aid social engineering efforts.
Mitigation strategies focus heavily on timely software updates and strict adherence to security patching cycles. Users must ensure they are running Firefox version 154, Firefox Extended Support Release (ESR) version 140.14, or ESR version 153.1 or later, as these releases contain the necessary code corrections to resolve the focus handling logic errors. For organizations deploying Firefox at scale, implementing automated patch management systems is critical to ensure all endpoints receive this security update promptly. Additionally, developers should review their use of DOM event listeners and avoid exposing internal browser states through custom APIs that might inadvertently bypass existing sandboxing mechanisms.
This incident aligns with the MITRE ATT&CK framework technique T1078 Valid Accounts or potentially T1539 Steal Web Session Cookie depending on how the leaked information is utilized, though it primarily falls under reconnaissance phases like T1418 New Technique for Defense Evasion if used to bypass detection. Security teams should monitor browser update telemetry and enforce policies that prevent downgrade attacks which could expose users to known vulnerabilities fixed in newer versions. Regular security audits of web applications hosted within corporate environments can also help identify potential exploitation vectors before they are weaponized by external adversaries seeking to leverage such information disclosure flaws for deeper penetration into target networks.