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CVE-2025-6425

The WebCompat WebExtension shipped with Firefox exposed a persistent UUID

CVSS 4.3 MEDIUMEPSS 0.2%CWE-200
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.
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N
Affected products
Mozilla · FirefoxMozilla · Thunderbird

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References
https://bugzilla.mozilla.org/show_bug.cgi?id=1717672https://lists.debian.org/debian-lts-announce/2025/06/msg00029.htmlhttps://lists.debian.org/debian-lts-announce/2025/07/msg00002.htmlhttps://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/