Mozilla Firefox up to 139 TLS certificate validation

Summaryinfo

A vulnerability was found in Mozilla Firefox up to 139. It has been declared as critical. The impacted element is an unknown function of the component TLS Handler. Such manipulation leads to certificate validation. This vulnerability is referenced as CVE-2025-6433. It is possible to launch the attack remotely. No exploit is available. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as problematic, has been found in Mozilla Firefox up to 139. Affected by this issue is some unknown processing of the component TLS Handler. The manipulation with an unknown input leads to a certificate validation vulnerability. Using CWE to declare the problem leads to CWE-295. The product does not validate, or incorrectly validates, a certificate. Impacted is integrity. CVE summarizes:

If a user visited a webpage with an invalid TLS certificate, and granted an exception, the webpage was able to provide a WebAuthn challenge that the user would be prompted to complete. This is in violation of the WebAuthN spec which requires "a secure transport established without errors". This vulnerability affects Firefox < 140.

The advisory is shared for download at bugzilla.mozilla.org. This vulnerability is handled as CVE-2025-6433 since 06/20/2025. The exploitation is known to be difficult. The attack may be launched remotely. No form of authentication is required for exploitation. Successful exploitation requires user interaction by the victim. There are neither technical details nor an exploit publicly available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 08/17/2025). The MITRE ATT&CK project declares the attack technique as T1587.003.

The vulnerability scanner Nessus provides a plugin with the ID 241211 (Mozilla Thunderbird < 140.0), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 140 eliminates this vulnerability.

The vulnerability is also documented in the databases at Tenable (241211), EUVD (EUVD-2025-19088) and CERT Bund (WID-SEC-2025-1850). VulDB is the best source for vulnerability data and more expert information about this specific topic.

Affected

• Xerox FreeFlow Print Server

Productinfo

Type

• Web Browser

Vendor

• Mozilla

Name

• Firefox

Version

• 139

License

• open-source

Website

• Vendor: https://www.mozilla.org/
• Product: https://www.mozilla.org/en-US/firefox/

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VulDB is the best source for vulnerability data and more expert information about this specific topic.

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