CVE-2020-26979 in Firefox
Summary
by MITRE • 01/07/2021
When a user typed a URL in the address bar or the search bar and quickly hit the enter key, a website could sometimes capture that event and then redirect the user before navigation occurred to the desired, entered address. To construct a convincing spoof the attacker would have had to guess what the user was typing, perhaps by suggesting it. This vulnerability affects Firefox < 84.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 05/25/2026
This vulnerability represents a sophisticated client-side attack vector that exploits timing discrepancies in browser navigation handling mechanisms. The flaw occurs when users rapidly input URLs in address bars or search interfaces and immediately press enter, creating a window where malicious websites can intercept and manipulate the navigation process before the intended destination is reached. This type of vulnerability falls under the category of timing-based injection attacks and can be classified as a race condition vulnerability. The attack exploits the temporal gap between user input recognition and actual navigation initiation, allowing attackers to capture the intended URL before the browser processes it.
The technical implementation of this vulnerability relies on the browser's event handling system and its response to rapid user interactions. When a user types quickly and hits enter immediately, the browser's input processing pipeline may not have fully synchronized the URL capture with the navigation execution. This creates an opportunity for malicious web pages to register event listeners that intercept the navigation intent and redirect users to attacker-controlled domains. The vulnerability specifically affects Firefox versions prior to 84, indicating that the issue was related to how the browser's navigation stack handled rapid successive events during the URL processing lifecycle.
The operational impact of this vulnerability extends beyond simple phishing attempts, as it enables sophisticated social engineering attacks that can masquerade as legitimate navigation processes. Attackers can craft convincing spoofing scenarios by predicting or capturing user input patterns, making the redirection appear more authentic to victims. This vulnerability aligns with attack patterns documented in the attack tree framework where timing-based manipulation can be used to bypass user intent verification mechanisms. The security implications are particularly severe because users may unknowingly navigate to malicious sites while believing they are visiting legitimate destinations, creating a false sense of security during the navigation process.
Mitigation strategies for this vulnerability require comprehensive browser-side fixes that address the timing gap in navigation handling. The solution involves implementing proper synchronization mechanisms between input capture and navigation execution to prevent premature redirection. Security researchers have recommended that browsers establish robust input validation and event handling protocols that ensure user intent is properly captured and preserved during rapid interaction scenarios. Organizations should implement immediate patching procedures for affected Firefox versions and consider browser hardening measures that include enhanced event queue management and input validation controls. This vulnerability demonstrates the importance of considering temporal aspects in security design and aligns with recommendations in the OWASP Top Ten for addressing timing-based attacks that exploit browser event processing behaviors.