Medium severity · published Sep 30, 2026
CVE-2026-103500
Heap buffer overflow opening large email
6.1
CVSS
0.3%
EPSS
No
On KEV
Description
An attacker could cause a heap buffer overflow by getting a user to open an email that is greater than or equal to 2GB in size. This vulnerability was fixed in Thunderbird 157, Thunderbird 140.17, and Thunderbird 153.4.
CVSS vector
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:H
Attack vector
Local
Complexity
Low
Privileges
None
User interaction
Required
Confidentiality
None
Integrity
Low
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.3% · higher than 20% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
TH
Thunderbird · Mozilla
before 140.17.0; 141.0 before 153.4.0; 154.0 before 157.0 · source: NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-103500
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-103500
bugzilla.mozilla.org
https://bugzilla.mozilla.org/show_bug.cgi?id=2070267
www.mozilla.org
https://www.mozilla.org/security/advisories/mfsa2026-101/
www.mozilla.org
https://www.mozilla.org/security/advisories/mfsa2026-102/
www.mozilla.org
https://www.mozilla.org/security/advisories/mfsa2026-103/
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