CVE-2026-74989: Internally found bugs fixed in Firefox 154

Severity: critical (CVSS 9.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.6% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-08-18 · updated 2026-10-28
Weakness: CWE-119

Description

Internally found bugs present in Firefox 153. Some of these bugs showed evidence of memory corruption or another security-relevant defect and we presume that with enough effort some of these could have been exploited. This vulnerability was fixed in Firefox 154 and Thunderbird 154.

Affected products

Mozilla Firefox: before 154.0.0 — fixed in 154.0.0
Mozilla Thunderbird: before 154.0 — fixed in 154.0

How to fix

Upgrade to a fixed version: Mozilla Firefox 154.0.0; Mozilla Thunderbird 154.0. Check the vendor advisory for mitigations.

References

https://bugzilla.mozilla.org/buglist.cgi?bug_id=2022257%2C2027351%2C2027380%2C2029289
https://bugzilla.mozilla.org/buglist.cgi?bug_id=2027388%2C2029750%2C2029794%2C2043298%2C2045126%2C2049810%2C2051741
https://www.mozilla.org/security/advisories/mfsa2026-74/
https://www.mozilla.org/security/advisories/mfsa2026-78/

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