What’s Vulnerable › Vulnerabilities

CVE-2026-12327: Memory safety bugs fixed in Firefox ESR 140.12, Thunderbird ESR 140.12, Firefox 152 and Thunderbird 152

• Severity: high (CVSS 8.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% 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

Memory safety bugs present in Firefox ESR 140.11, Thunderbird ESR 140.11, Firefox 151 and Thunderbird 151. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability was fixed in Firefox 152, Firefox ESR 140.12, Thunderbird 152, and Thunderbird 140.12.

Affected products

• Mozilla Firefox: before 115.37.0; before 152.0.0; from 140.0 before 140.12.0 — fixed in 115.37.0, 152.0.0, 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, 152.0.0, 140.12.0; Mozilla Thunderbird 152.0.0, 140.12.0. Check the vendor advisory for mitigations.

References

• https://bugzilla.mozilla.org/buglist.cgi?bug_id=2011842%2C2023902%2C2025512%2C2027312%2C2029444%2C2036571%2C2036900%2C2036936%2C2037995%2C2038551%2C2040717%2C2042724
• https://www.mozilla.org/security/advisories/mfsa2026-57/
• https://www.mozilla.org/security/advisories/mfsa2026-58/
• https://www.mozilla.org/security/advisories/mfsa2026-60/
• https://www.mozilla.org/security/advisories/mfsa2026-61/

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