CVE-2026-74989

CRITICAL 9.8

Internally found bugs fixed in Thunderbird 154

CVSS Score

9.8

EPSS Score

0.3%

EPSS Percentile

26th

Internally found bugs present in Thunderbird 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.

Vendor	mozilla
Product	firefox
Ecosystems	Browser JavaScript
Industries	Technology
Published	Aug 18, 2026
Last Updated	Sep 1, 2026

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Affected Versions

Mozilla / Firefox

All versions affected

Mozilla / Thunderbird

All versions affected

References

NVD ↗ CVE.org ↗ EPSS Data ↗

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

Credits

Christian Holler, Ryan Hunt, Tom Ritter and the Mozilla Fuzzing Team