What’s Vulnerable › Vulnerabilities

CVE-2025-6425: The WebCompat WebExtension shipped with Firefox exposed a persistent UUID

• Severity: medium (CVSS 4.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2025-06-24 · updated 2026-10-23
• Weakness: CWE-200

Description

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 was fixed in Firefox 140, Firefox ESR 115.25, Firefox ESR 128.12, Thunderbird 140, and Thunderbird 128.12.

Affected products

• Mozilla Firefox: before 115.25.0; before 140.0; from 116.0 before 128.12.0 — fixed in 115.25.0, 128.12.0, 140.0

How to fix

Upgrade to a fixed version: Mozilla Firefox 115.25.0, 128.12.0, 140.0. Check the vendor advisory for mitigations.

References

• https://bugzilla.mozilla.org/show_bug.cgi?id=1717672
• https://www.mozilla.org/security/advisories/mfsa2025-51/
• https://www.mozilla.org/security/advisories/mfsa2025-52/
• https://www.mozilla.org/security/advisories/mfsa2025-53/
• https://www.mozilla.org/security/advisories/mfsa2025-54/
• https://www.mozilla.org/security/advisories/mfsa2025-55/
• https://lists.debian.org/debian-lts-announce/2025/06/msg00029.html
• https://lists.debian.org/debian-lts-announce/2025/07/msg00002.html

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