Mozilla Firefox up to 139 WebCompat Extension information disclosure

Summaryinfo

A vulnerability classified as problematic has been found in Mozilla Firefox up to 139. Affected by this vulnerability is an unknown functionality of the component WebCompat Extension. This manipulation causes information disclosure. This vulnerability appears as CVE-2025-6425. The attack may be initiated remotely. There is no available exploit. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability has been found in Mozilla Firefox up to 139 and classified as problematic. Affected by this vulnerability is some unknown processing of the component WebCompat Extension. The manipulation with an unknown input leads to a information disclosure vulnerability. The CWE definition for the vulnerability is CWE-200. The product exposes sensitive information to an actor that is not explicitly authorized to have access to that information. As an impact it is known to affect confidentiality. The summary by CVE is:

An attacker who enumerated resources from the WebCompat extension could have obtained a persistent UUID that identified the browser, and persisted between containers and normal/private browsing mode, but not profiles. This vulnerability affects Firefox < 140, Firefox ESR < 115.25, and Firefox ESR < 128.12.

The advisory is shared at bugzilla.mozilla.org. This vulnerability is known as CVE-2025-6425 since 06/20/2025. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. It demands that the victim is doing some kind of user interaction. Neither technical details nor an exploit are publicly available. The price for an exploit might be around USD $0-$5k at the moment (estimation calculated on 07/30/2025). MITRE ATT&CK project uses the attack technique T1592 for this issue.

The vulnerability scanner Nessus provides a plugin with the ID 240338 (Mozilla Firefox ESR < 115.25), 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 (240338), EUVD (EUVD-2025-19101) and CERT Bund (WID-SEC-2025-1395). Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Affected

• Debian Linux
• Amazon Linux 2
• Red Hat Enterprise Linux
• Fedora Linux
• Ubuntu Linux
• SUSE Linux
• Oracle Linux
• SUSE openSUSE
• IGEL OS
• Mozilla Firefox
• Mozilla Firefox ESR
• Mozilla Thunderbird

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/

CPE 2.3info

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Entryinfo

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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