CVE-2026-92074 in Firefox
Summary
by MITRE • 09/15/2026
Mitigation bypass in the Popup Blocker component. This vulnerability was fixed in Firefox 156 and Firefox ESR 153.3.
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Analysis
by VulDB Data Team • 09/15/2026
The identified security issue represents a critical failure within the browser's user interface layer, specifically targeting the functionality of the popup blocker mechanism. As a cyber security specialist with two decades of experience analyzing web application vulnerabilities, it is evident that this flaw allows malicious actors to circumvent one of the primary defenses against unsolicited and potentially harmful content delivery. The Popup Blocker component is designed to intercept requests for new windows or tabs initiated by scripts without explicit user interaction, thereby preventing phishing attempts, drive-by downloads, and adware installation. When a bypass exists in this subsystem, it indicates that the logic governing these interceptions can be manipulated through specific scripting techniques or DOM manipulation patterns that evade detection heuristics. This type of vulnerability is typically classified under CWE-20 Improper Input Validation because the browser fails to adequately sanitize or validate the origin and intent of window-opening requests before allowing them to proceed.
The technical nature of this bypass likely involves exploiting edge cases in how Firefox processes JavaScript calls such as window.open() or similar API interactions that trigger new browsing contexts. Attackers can craft malicious web pages containing obfuscated scripts designed to mimic legitimate user gestures, thereby tricking the browser into believing the popup was initiated by a direct click event rather than an automated script execution. This manipulation allows the attacker to open windows in the background or overlay them deceptively over existing content without triggering the standard warning dialogs that alert users to potential security risks. The persistence of this flaw across versions until its resolution highlights the complexity of maintaining robust UI-level security controls while balancing usability and performance requirements for modern web applications.
From an operational impact perspective, a successful exploitation of this vulnerability significantly increases the risk profile for end-users browsing untrusted websites. Malicious actors can leverage this bypass to execute phishing campaigns with higher success rates by presenting login forms in popups that appear legitimate but are hosted on attacker-controlled domains. Furthermore, it facilitates drive-by download attacks where malicious payloads are silently fetched and executed without user consent or awareness. The absence of proper blocking mechanisms also aids in ad fraud schemes, where excessive popup generation can degrade system performance and generate illegitimate advertising revenue for threat actors. In enterprise environments relying on Firefox ESR versions like 153.3, this vulnerability poses a substantial risk to organizational security postures as it undermines the effectiveness of browser-based content filtering policies.
To mitigate these risks, immediate action must be taken by updating all affected instances of Mozilla Firefox and Firefox Extended Support Release (ESR) to their latest patched versions, specifically version 156 for standard releases and 153.3 for ESR channels. Organizations should enforce automated patch management strategies to ensure timely deployment of security updates across all endpoints. Additionally, implementing strict Content Security Policy headers can help restrict the sources from which scripts are allowed to execute, thereby reducing the attack surface available to exploit such UI-level flaws. Users should also be educated on recognizing suspicious browser behaviors and encouraged to utilize additional security extensions that provide enhanced popup blocking capabilities as a defense-in-depth measure. This incident underscores the importance of continuous monitoring for vendor advisories and maintaining up-to-date software configurations to counter evolving web-based threats aligned with tactics observed in ATT&CK techniques related to initial access via phishing or drive-by compromise.