CVE-2025-5266

MEDIUM 4.3CVE-2025-5266 · Published 27/05/2025 · updated 05/10/2026

In short

CVE-2025-5266 is a MEDIUM (CVSS 4.3) vulnerability affecting firefox (mozilla).
Chance of exploitation in the next 30 days (EPSS): 0.34%, higher than 27.7% of all vulnerabilities.
Fix: update to 128.11.0, 139.0 or later.

Package	Affected versions	Patched versions
firefox mozilla	`< 128.11.0< 139.0`	`128.11.0139.0`

Description

Script elements loading cross-origin resources generated load and error events which leaked information enabling XS-Leaks attacks. This vulnerability was fixed in Firefox 139, Firefox ESR 128.11, Thunderbird 139, and Thunderbird 128.11.

References

bugzilla.mozilla.org/show_bug.cgi · Permissions Required
mozilla.org/security/advisories/mfsa2025-42 · Vendor Advisory
mozilla.org/security/advisories/mfsa2025-44 · Vendor Advisory
mozilla.org/security/advisories/mfsa2025-45
mozilla.org/security/advisories/mfsa2025-46
lists.debian.org/debian-lts-announce/2025/05/msg00043.html
lists.debian.org/debian-lts-announce/2025/05/msg00046.html

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Package

Affected versions

Patched versions

firefox

mozilla

< 128.11.0< 139.0

128.11.0139.0

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