CVE-2025-10529: Same-origin policy bypass in the Layout component

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-09-16 · updated 2026-10-23
Weakness: CWE-942

Description

Same-origin policy bypass in the Layout component. This vulnerability was fixed in Firefox 143, Firefox ESR 140.3, Thunderbird 143, and Thunderbird 140.3.

Affected products

Mozilla Firefox: before 140.3.0; before 143.0 — fixed in 140.3.0, 143.0
Mozilla Thunderbird: before 143.0 — fixed in 143.0

How to fix

Upgrade to a fixed version: Mozilla Firefox 140.3.0, 143.0; Mozilla Thunderbird 143.0. Check the vendor advisory for mitigations.

References

https://bugzilla.mozilla.org/show_bug.cgi?id=1970490
https://www.mozilla.org/security/advisories/mfsa2025-73/
https://www.mozilla.org/security/advisories/mfsa2025-75/
https://www.mozilla.org/security/advisories/mfsa2025-77/
https://www.mozilla.org/security/advisories/mfsa2025-78/
https://lists.debian.org/debian-lts-announce/2025/09/msg00020.html
https://lists.debian.org/debian-lts-announce/2025/09/msg00026.html

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