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MEDIUM

CVE-2025-5266

CVSS v3

4.3

MEDIUM

EPSS Score

0.3 %

exploit probability, as of 2026-10-19

CISA KEV

No

known exploited

Exploitation

—

SSVC status

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Affected and fixed versions

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

  • firefoxAlmaLinux:10all versions · fixed in 128.11.0-1.el10_0
  • firefoxAlmaLinux:9all versions · fixed in 128.11.0-1.el9_6.alma.1and 2 other packages
  • firefoxAlmaLinux:8all versions · fixed in 128.11.0-1.el8_10.alma.1and 1 other package
  • thunderbirdAlmaLinux:10all versions · fixed in 128.11.0-1.el10_0.alma.1

Vendor advisories

  • CVE-2025-5266 Red Hat Product Security249 products fixed · 8 known affected

    firefox: thunderbird: Script element events leaked cross-origin resource status

    rhel10/firefox-flatpak.src as a component of Red Hat Enterprise Linux 10 · rhel10/thunderbird-flatpak.src as a component of Red Hat Enterprise Linux 10 · firefox as a component of Red Hat Enterprise Linux 6

  • RHSA-2025:9155 Red Hat Product Security21 products fixed

    Red Hat Security Advisory: firefox security update

  • RHSA-2025:9072 Red Hat Product Security17 products fixed

    Red Hat Security Advisory: firefox security update

  • RHSA-2025:9071 Red Hat Product Security17 products fixed

    Red Hat Security Advisory: firefox security update

  • RHSA-2025:9077 Red Hat Product Security7 products fixed

    Red Hat Security Advisory: firefox security update

  • RHSA-2025:9074 Red Hat Product Security5 products fixed

    Red Hat Security Advisory: firefox security update

16 more advisories

Full record on NVD

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.

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N
Published
2025-05-27
Last Modified
2026-04-13

Frequently asked questions

What is CVE-2025-5266?

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.

Is CVE-2025-5266 actively exploited?

Active exploitation of CVE-2025-5266 has not been confirmed. Its EPSS score was 0.3% on 2026-10-19, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2025-5266?

CVE-2025-5266 has a CVSS v3 base score of 4.3 (MEDIUM severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N.

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