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CVE-2026-12329: Memory safety bug fixed in Thunderbird ESR 140.12

• Severity: medium (CVSS 5.3 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: 2026-06-16 · updated 2026-10-25
• Weakness: CWE-119

Description

Memory safety bug fixed in Thunderbird ESR 140.12. This vulnerability was fixed in Firefox ESR 140.12 and Thunderbird 140.12.

Affected products

• Mozilla Firefox: from 140.0 before 140.12.0 — fixed in 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 140.12.0; Mozilla Thunderbird 140.12.0. Check the vendor advisory for mitigations.

References

• https://bugzilla.mozilla.org/show_bug.cgi?id=2044738
• https://www.mozilla.org/security/advisories/mfsa2026-58/
• https://www.mozilla.org/security/advisories/mfsa2026-61/
• https://access.redhat.com/errata/RHSA-2026:27717
• https://access.redhat.com/errata/RHSA-2026:27733
• https://access.redhat.com/errata/RHSA-2026:27734
• https://access.redhat.com/errata/RHSA-2026:29940
• https://access.redhat.com/errata/RHSA-2026:30846
• https://access.redhat.com/errata/RHSA-2026:33445
• https://access.redhat.com/errata/RHSA-2026:36100
• https://access.redhat.com/errata/RHSA-2026:36101
• https://access.redhat.com/errata/RHSA-2026:36102

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