CVE-2026-12330: Incorrect boundary conditions in the Internationalization component

Severity: medium (CVSS 5.4 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-06-16 · updated 2026-10-26
Weakness: CWE-119

Description

Incorrect boundary conditions in the Internationalization component. This vulnerability was fixed in Firefox ESR 140.12, Firefox ESR 115.37, and Thunderbird 140.12.

Affected products

Mozilla Firefox: before 115.37.0; from 140.0 before 140.12.0 — fixed in 115.37.0, 140.12.0
Mozilla Thunderbird: from 140.0 before 140.12.0 — fixed in 140.12.0

How to fix

Upgrade to a fixed version: Mozilla Firefox 115.37.0, 140.12.0; Mozilla Thunderbird 140.12.0. Check the vendor advisory for mitigations.

References

https://bugzilla.mozilla.org/show_bug.cgi?id=2029326
https://www.mozilla.org/security/advisories/mfsa2026-58/
https://www.mozilla.org/security/advisories/mfsa2026-59/
https://www.mozilla.org/security/advisories/mfsa2026-61/

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