CVE-2026-84142

Internally found bugs present in Thunderbird 154. 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 155 and Thunderbird 155.

  • Published Sep 1, 2026
  • CVSS 9.8 critical
  • 0.6% chance of exploitation in the next 30 days (EPSS)
  • A fix is available

Affected software

CVE-2026-84142 at the National Vulnerability Database