What’s Vulnerable › Vulnerabilities

CVE-2026-0891: Memory safety bugs fixed in Firefox ESR 140.7, Thunderbird ESR 140.7, Firefox 147 and Thunderbird 147

• Severity: high (CVSS 8.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-01-13 · updated 2026-07-15
• Weakness: CWE-119

Description

Memory safety bugs present in Firefox ESR 140.6, Thunderbird ESR 140.6, Firefox 146 and Thunderbird 146. 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 147, Firefox ESR 140.7, Thunderbird 147, and Thunderbird 140.7.

Affected products

• Mozilla Firefox: before 140.7.0; before 147.0 — fixed in 140.7.0, 147.0
• Mozilla Thunderbird: before 140.7.0; before 147.0 — fixed in 140.7.0, 147.0

How to fix

Upgrade to a fixed version: Mozilla Firefox 140.7.0, 147.0; Mozilla Thunderbird 140.7.0, 147.0. Check the vendor advisory for mitigations.

References

• https://bugzilla.mozilla.org/buglist.cgi?bug_id=1964722%2C2000981%2C2003100%2C2003278
• https://www.mozilla.org/security/advisories/mfsa2026-01/
• https://www.mozilla.org/security/advisories/mfsa2026-03/
• https://www.mozilla.org/security/advisories/mfsa2026-04/
• https://www.mozilla.org/security/advisories/mfsa2026-05/
• https://access.redhat.com/errata/RHSA-2026:0667
• https://access.redhat.com/errata/RHSA-2026:0694
• https://access.redhat.com/errata/RHSA-2026:0924
• https://access.redhat.com/errata/RHSA-2026:1320
• https://access.redhat.com/errata/RHSA-2026:1413
• https://access.redhat.com/errata/RHSA-2026:1414
• https://access.redhat.com/errata/RHSA-2026:1415

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