Critical severity · published Aug 18, 2026
CVE-2026-74989
Internally found bugs fixed in Thunderbird 154
9.8
CVSS
0.6%
EPSS
No
On KEV
Description
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
High
Integrity
High
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.6% · higher than 47% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
FI
Firefox · Mozilla
before 154.0.0 · source: NVD
TH
Thunderbird · Mozilla
before 154.0 · source: NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-74989
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-74989
Not Applicable
https://bugzilla.mozilla.org/buglist.cgi?bug_id=2022257%2C2027351%2C2027380%2C2029289
Not Applicable
https://bugzilla.mozilla.org/buglist.cgi?bug_id=2027388%2C2029750%2C2029794%2C2043298%2C2045126%2C2049810%2C2051741
Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-74/
Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-78/
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