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CVE-2026-12299: JIT miscompilation in the DOM: Core & HTML component

• Severity: medium (CVSS 5.4 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 2026-10-26
• Weakness: CWE-843

Description

JIT miscompilation in the DOM: Core & HTML component. This vulnerability was fixed in Firefox 152, Firefox ESR 140.12, Firefox ESR 115.37, Thunderbird 152, and Thunderbird 140.12.

Affected products

• Mozilla Firefox: before 115.37.0; before 152.0; from 140.0 before 140.12.0 — fixed in 115.37.0, 152.0, 140.12.0
• Mozilla Thunderbird: before 152.0.0; from 140.0 before 140.12.0 — fixed in 152.0.0, 140.12.0

How to fix

Upgrade to a fixed version: Mozilla Firefox 115.37.0, 152.0, 140.12.0; Mozilla Thunderbird 152.0.0, 140.12.0. Check the vendor advisory for mitigations.

References

• https://bugzilla.mozilla.org/show_bug.cgi?id=2043139
• https://www.mozilla.org/security/advisories/mfsa2026-57/
• https://www.mozilla.org/security/advisories/mfsa2026-58/
• https://www.mozilla.org/security/advisories/mfsa2026-59/
• https://www.mozilla.org/security/advisories/mfsa2026-60/
• 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

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