What’s Vulnerable › Vulnerabilities

CVE-2026-84637: Calendar invitation attachments could launch local executables

• Severity: critical (CVSS 9.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.6% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-09-01 · updated 2026-09-03
• Weakness: CWE-434

Description

Malicious calendar invitations could use file URI attachments to launch local or network-hosted executables on Windows, bypassing Thunderbird's normal executable attachment protections. With the new invitation display enabled, the attachment could also appear under a misleading filename. This vulnerability was fixed in Thunderbird 154 and Thunderbird 153.2.

Affected products

• Mozilla Thunderbird: before 153.2.0; from 154.0 before 155.0 — fixed in 153.2.0, 155.0

How to fix

Upgrade to a fixed version: Mozilla Thunderbird 153.2.0, 155.0. Check the vendor advisory for mitigations.

References

• https://bugzilla.mozilla.org/show_bug.cgi?id=2043878
• https://www.mozilla.org/security/advisories/mfsa2026-78/
• https://www.mozilla.org/security/advisories/mfsa2026-88/

Get alerted when CVE-2026-84637 or the next vulnerability affects your stack