CVE-2025-5266 Affecting firefox-esr package, versions <128.11-r0


Severity

Recommended
low

Based on default assessment until relevant scores are available.

Threat Intelligence

EPSS
0.29% (21st percentile)

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  • Snyk IDSNYK-CHAINGUARDLATEST-FIREFOXESR-17764052
  • published1 Jul 2026
  • disclosed27 May 2025

Introduced: 27 May 2025

CVE-2025-5266  (opens in a new tab)

How to fix?

Upgrade Chainguard firefox-esr to version 128.11-r0 or higher.

NVD Description

Note: Versions mentioned in the description apply only to the upstream firefox-esr package and not the firefox-esr package as distributed by Chainguard. See How to fix? for Chainguard relevant fixed versions and status.

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.

CVSS Base Scores

version 3.1