All vulnerabilities
CVE-2026-103500

Thunderbird: Heap buffer overflow opening large email

Mozilla Thunderbird
Open in ThreatlineRecord JSON
CVSS
6.3Medium
ExploitationNo known exploitationNot in CISA KEV, which does not prove it is unexploitedCISA KEV
Exploit odds (EPSS)0.21%Chance of exploitation activity in the next 30 days, higher than 11% of CVEs. Scored 23 Oct 2026FIRST EPSS
Fixed inNone listedNo source names a fixed version. Check the vendor advisory below
Published30 Sep 2026Updated 21 Oct 2026CVE List

What fixes it

No source in this snapshot names a fixed version. The vendor advisories under References are the place to check.

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.

Text from CVE List

Affected versions 3

  • Thunderbirdunaffected: 140.17 through 140.*CVE List
  • Thunderbirdunaffected: 153.4 through 153.*CVE List
  • Thunderbirdunaffected: 157CVE List

References 4