CVE-2023-6211 in Firefox
Summary
by MITRE • 11/21/2023
If an attacker needed a user to load an insecure http: page and knew that user had enabled HTTPS-only mode, the attacker could have tricked the user into clicking to grant an HTTPS-only exception if they could get the user to participate in a clicking game. This vulnerability affects Firefox < 120.
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Analysis
by VulDB Data Team • 08/17/2025
This vulnerability represents a sophisticated user deception attack that exploits the interaction between Firefox's security features and user behavior patterns. The flaw specifically targets Firefox versions prior to 120 where the browser's HTTPS-only mode functionality creates an unexpected security boundary that attackers can manipulate through social engineering techniques. When users have HTTPS-only mode enabled, the browser typically blocks insecure http: connections and prompts users to manually approve exceptions for specific sites. However, this vulnerability allows attackers to craft malicious scenarios where users might be tricked into inadvertently approving these exceptions through carefully orchestrated clicking sequences.
The technical mechanism behind this vulnerability involves the browser's handling of mixed content scenarios and user interaction prompts within the HTTPS-only mode framework. When a user attempts to access an http: page while HTTPS-only mode is active, Firefox presents a security warning that requires explicit user action to proceed. Attackers can exploit this by creating web pages that present multiple clicking options or by using timing attacks where the user's natural clicking behavior is manipulated to inadvertently select the exception approval option. This attack vector leverages the user's trust in the browser's security warnings and their tendency to follow familiar clicking patterns without fully understanding the security implications.
The operational impact of this vulnerability extends beyond simple credential theft or data interception. It represents a significant bypass of Firefox's intended security posture where the browser's protection mechanisms are circumvented through social engineering rather than technical exploitation. Users who have explicitly enabled HTTPS-only mode for enhanced security are placed at risk because the vulnerability assumes that attackers can manipulate user behavior to approve exceptions. This creates a dangerous precedent where users who believe they have strengthened their security posture through HTTPS-only mode can be tricked into weakening that protection through seemingly innocuous user interactions.
From a security standards perspective, this vulnerability aligns with CWE-693 Protection Mechanism Failure, as it demonstrates how user interaction prompts can be manipulated to bypass intended security controls. The attack pattern also reflects techniques described in the MITRE ATT&CK framework under T1566 Initial Access - Phishing, specifically targeting user behavior manipulation rather than technical system exploitation. The vulnerability essentially creates a false sense of security where users believe they are protected by their browser's security settings, while attackers can exploit the natural user interaction patterns to gain unauthorized access to insecure content. Organizations should consider this when implementing security awareness training, as it highlights the need for users to understand not just technical security features but also how attackers can manipulate user interactions with these features.
The mitigation strategy for this vulnerability requires immediate browser updates to Firefox version 120 or later where the security flaw has been addressed. Additionally, security teams should implement enhanced user education programs that emphasize the importance of carefully reviewing security prompts and understanding that clicking through security warnings can compromise their protection. Network administrators should consider implementing additional content filtering mechanisms to prevent access to known malicious domains, while security monitoring should include detection of unusual user behavior patterns that might indicate successful exploitation attempts. The vulnerability also underscores the importance of conducting regular security assessments of browser security features to ensure that user interaction patterns don't create unintended attack vectors that could be exploited by adversaries.