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
References8
- bugzilla.mozilla.org/show_bug.cgi?id=1717672 Issue TrackingVendor Advisory
- www.mozilla.org/security/advisories/mfsa2025-51/ Vendor Advisory
- www.mozilla.org/security/advisories/mfsa2025-52/ Vendor Advisory
- www.mozilla.org/security/advisories/mfsa2025-53/ Vendor Advisory
- www.mozilla.org/security/advisories/mfsa2025-54/ Vendor Advisory
- www.mozilla.org/security/advisories/mfsa2025-55/ Vendor Advisory
- lists.debian.org/debian-lts-announce/2025/06/msg00029.html
- lists.debian.org/debian-lts-announce/2025/07/msg00002.html
Metrics
- CVSS 3.1
-
4.3
MEDIUM
Score source: CNA
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N - EPSS — exploit probability
- 0% percentile: 24 · as of 7 November 2026
- CWE
- CWE-200
Could this be exploited in your environment?
A patch closes the known hole. A penetration test shows what an attacker can still reach — with proof.