CVE-2025-6434 in Firefox
Summary
by MITRE • 06/24/2025
The exception page for the HTTPS-Only feature, displayed when a website is opened via HTTP, lacked an anti-clickjacking delay, potentially allowing an attacker to trick a user into granting an exception and loading a webpage over HTTP. This vulnerability affects Firefox < 140.
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Analysis
by VulDB Data Team • 08/17/2025
The vulnerability described in CVE-2025-6434 represents a significant security flaw in Firefox's implementation of the HTTPS-Only feature, specifically within the exception handling mechanism for HTTP connections. This issue stems from the absence of proper anti-clickjacking protections in the user interface element that prompts users when they attempt to access websites via HTTP protocols. The vulnerability is particularly concerning because it directly targets the browser's security model designed to protect users from man-in-the-middle attacks and protocol downgrade scenarios that could expose sensitive data to interception.
The technical flaw manifests in the exception page's user interface design, which should have implemented a delay mechanism to prevent automated clickjacking attacks. Without this anti-clickjacking delay, attackers can exploit the timing of user interactions to manipulate the browser's security behavior through malicious web pages that appear to be legitimate sites. This vulnerability operates under the broader category of web security flaws that compromise user intent and browser security policies, specifically targeting the user interaction model that should protect against automated manipulation of security decisions.
From an operational impact perspective, this vulnerability creates a pathway for attackers to bypass Firefox's HTTPS-Only protection mechanisms by tricking users into granting exceptions to HTTP connections. The attack vector relies on social engineering combined with clickjacking techniques where malicious actors can present a convincing interface that prompts users to click through security warnings, potentially leading to the loading of malicious HTTP content. This represents a direct threat to the integrity of the browser's security model and can result in data exposure, session hijacking, and other protocol-level attacks that undermine the security assurances provided by HTTPS.
The vulnerability aligns with several established security frameworks including CWE-346, which addresses "Origin Validation Error" and related issues in web application security where proper validation of user interactions and interface elements is critical. Additionally, this flaw relates to ATT&CK technique T1211, which involves "Exploitation for Defense Evasion" through manipulation of user interface elements to bypass security controls. The lack of proper timing controls and anti-clickjacking measures in the exception page demonstrates a failure in implementing proper user interface security patterns that should prevent malicious manipulation of security decisions.
Organizations and users should immediately update to Firefox version 140 or later to mitigate this vulnerability, as the fix likely includes the implementation of proper anti-clickjacking delays and enhanced validation of user interactions with security exception prompts. Security teams should also implement monitoring for suspicious user behavior patterns that might indicate exploitation attempts and consider additional network-level protections to detect and block attempts to downgrade connections from HTTPS to HTTP. The vulnerability serves as a reminder of the critical importance of securing all user interface elements in security-sensitive applications, as even seemingly minor interface components can provide attackers with significant exploitation opportunities.