CVE-2023-4053 in Firefox
Summary
by MITRE • 08/01/2023
A website could have obscured the full screen notification by using a URL with a scheme handled by an external program, such as a mailto URL. This could have led to user confusion and possible spoofing attacks. This vulnerability affects Firefox < 116.
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Analysis
by VulDB Data Team • 06/20/2025
This vulnerability represents a sophisticated UI overlay attack vector that exploits the interaction between web browsers and external application handlers. The flaw specifically manifests when a malicious website attempts to obscure full screen notifications by leveraging URLs with schemes that trigger external programs, most notably mailto URLs. This technique allows attackers to manipulate the user interface in ways that can deceive users about the true nature of their browsing environment. The vulnerability stems from Firefox's handling of URI schemes that are intended to launch external applications, creating an unexpected interaction when these schemes are embedded within full screen notification contexts.
The technical implementation of this vulnerability exploits the browser's protocol handling mechanism and user interface rendering priorities. When a website loads content that includes a URL with an external scheme such as mailto:, the browser may attempt to launch the associated application while simultaneously attempting to display a full screen notification. This creates a race condition or priority conflict where the external application handler can interfere with the notification display, potentially obscuring critical security warnings or legitimate user interface elements. The vulnerability specifically affects Firefox versions prior to 116, indicating that the issue was present in the browser's URI processing and window management components, particularly in how it handles the interaction between web content and system-level application handlers.
The operational impact of this vulnerability extends beyond simple user confusion to potentially enable sophisticated spoofing attacks that could deceive users into believing they are interacting with legitimate system interfaces rather than malicious web content. Attackers could craft web pages that appear to display security warnings or system notifications while actually routing users to external applications through concealed mailto links, effectively creating a false sense of security. This type of attack could be particularly dangerous in phishing scenarios where users might be tricked into providing sensitive information or performing actions they would not normally consent to. The vulnerability creates a situation where users cannot reliably distinguish between genuine browser notifications and those that have been obscured or manipulated by external application handlers, undermining the fundamental security model of user interface integrity.
Security mitigations for this vulnerability involve implementing stricter controls over URI scheme handling within full screen contexts and establishing more robust priority mechanisms between browser notifications and external application launchers. The fix implemented in Firefox 116 likely involved modifying the browser's protocol handler registration and execution logic to prevent external application launches from interfering with critical user interface elements during full screen operations. This aligns with common security practices for preventing UI redressing attacks and maintaining user interface integrity as outlined in various security frameworks. Organizations should ensure all users are updated to Firefox 116 or later versions to mitigate this risk, while security teams should monitor for similar vulnerabilities in other browsers that may exhibit similar protocol handling behaviors. The vulnerability demonstrates the importance of considering cross-component interactions in browser security models and highlights how seemingly benign features like external protocol handlers can create unexpected security risks when combined with user interface elements. This type of vulnerability is categorized under CWE-611 and relates to attack patterns involving user interface manipulation and protocol handler abuse as documented in the ATT&CK framework's technique for UI redressing and phishing attacks.