CVE-2017-7817 in Firefox
Summary
by MITRE
A spoofing vulnerability can occur when a page switches to fullscreen mode without user notification, allowing a fake address bar to be displayed. This allows an attacker to spoof which page is actually loaded and in use. Note: This attack only affects Firefox for Android. Other operating systems are not affected. This vulnerability affects Firefox < 56.
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Analysis
by VulDB Data Team • 01/15/2021
This vulnerability represents a sophisticated spoofing attack that exploits the fullscreen mode behavior in Firefox for Android, creating a critical security risk through user interface manipulation. The flaw occurs when a web page programmatically transitions to fullscreen mode without proper user notification or consent, enabling attackers to display a convincing fake address bar that mimics the legitimate browser interface. This deceptive technique allows malicious actors to trick users into believing they are visiting a trusted website while actually navigating to an attacker-controlled page, fundamentally undermining the browser's security model and user trust mechanisms.
The technical implementation of this vulnerability stems from Firefox for Android's insufficient validation of fullscreen mode transitions and lack of proper user awareness mechanisms during these state changes. When a page invokes fullscreen mode, the browser should ideally require explicit user interaction or provide clear visual indicators about the transition, but this implementation flaw allows automatic fullscreen activation without user confirmation. The vulnerability specifically affects Firefox versions prior to 56, indicating that this was a known issue that required targeted patching within the browser's security framework. The attack vector relies on the browser's inability to distinguish between legitimate fullscreen requests and malicious attempts to deceive users through interface manipulation.
The operational impact of this vulnerability extends beyond simple phishing attacks, as it fundamentally compromises the browser's ability to maintain user trust and security awareness. Users who encounter this attack may unknowingly enter sensitive information on what appears to be a legitimate website but is actually controlled by an attacker. This spoofing capability enables sophisticated social engineering campaigns where attackers can create convincing facades of trusted banking, e-commerce, or social media sites. The vulnerability affects the core security model of web browsers by undermining the address bar as a reliable indicator of site authenticity, potentially leading to credential theft, financial fraud, and data compromise. This type of attack aligns with the ATT&CK framework's techniques for credential access and user execution, specifically targeting the user's trust in browser interface elements.
The mitigation for this vulnerability required Firefox developers to implement proper user consent mechanisms before fullscreen mode transitions and ensure that address bar information remains clearly visible and tamper-proof during fullscreen operations. This fix likely involved modifying the browser's fullscreen API behavior to require explicit user interaction before transitioning to fullscreen mode, implementing additional checks to prevent unauthorized address bar manipulation, and strengthening the visual distinction between legitimate and fake browser interfaces. The vulnerability's restriction to Firefox for Android indicates that desktop versions had already implemented proper safeguards, highlighting the importance of platform-specific security considerations in mobile browser implementations. Organizations should ensure all Firefox installations are updated to version 56 or later to prevent exploitation of this spoofing vulnerability, as the attack requires no special privileges beyond standard web browsing capabilities.
This vulnerability demonstrates how seemingly minor interface design decisions can create significant security risks, particularly in mobile environments where screen real estate limitations may encourage less secure implementation patterns. The issue relates to CWE-611, which addresses improper access control in web applications, and CWE-352, which covers cross-site request forgery vulnerabilities. The attack pattern follows established methods for bypassing browser security controls through user interface manipulation, representing a classic example of how attackers exploit human factors in security systems. Proper implementation of user consent requirements and interface integrity checks would have prevented this vulnerability from being exploited, emphasizing the need for comprehensive security testing of browser interface behaviors and user interaction patterns.