CVE-2025-6434
MediumCVSS 4.3Exploitation Probability (EPSS)
Low risk19th percentile - higher than 19% of all known CVEs
Summary
The exception page for the HTTPS-Only feature, displayed when a website is opened via HTTP, lacked an anti-clickjacking delay. An attacker could trick a user into granting an exception and loading a webpage over HTTP.
Risk Assessment
A user could be tricked into allowing an insecure HTTP connection, exposing them to data interception or man-in-the-middle attacks. The vulnerability was fixed in Firefox 140 and Thunderbird 140.
Recommendation
Update Firefox and Thunderbird to version 140 or later. After updating, ensure the HTTPS-Only feature is enabled.
Other vulnerabilities in Firefox
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Mozilla blocked compromised intermediate eMudhra certificates via OneCRL on October 17, and the list was distributed to clients via RemoteSettings the same day. This update contains the updated OneCRL block list, ensuring clients will block the compromised certificates even if RemoteSettings is disabled by policy or otherwise unavailable in the user's network environment. The vulnerability was fixed in Firefox 158.0.1, Firefox ESR 153.5.1, Firefox ESR 115.43.1, Thunderbird 158.0.1, and Thunderbird 153.5.1.
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- CVE-2026-109740Critical
Sandbox escape due to incorrect boundary conditions in the Widget: Win32 component. The flaw was fixed in Firefox 158, Firefox ESR 153.5, Thunderbird 158, and Thunderbird 153.5.
Original NVD description (English source)
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 was fixed in Firefox 140 and Thunderbird 140.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS