Critical severity · published Sep 1, 2026
CVE-2026-84637
Calendar invitation attachments could launch local executables
9.8
CVSS
0.6%
EPSS
No
On KEV
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.
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 50% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
TH
Thunderbird · Mozilla
before 153.2.0; 154.0 before 155.0 · source: NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-84637
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-84637
Permissions Required
https://bugzilla.mozilla.org/show_bug.cgi?id=2043878
Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-78/
Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-88/
More from Thunderbird
10.0
CVE-2019-11708
Mozilla Firefox and Thunderbird Sandbox Escape Vulnerability
9.8
CVE-2024-9680
Mozilla Firefox Use-After-Free Vulnerability
9.8
CVE-2010-3765
Mozilla Multiple Products Remote Code Execution Vulnerability
9.6
CVE-2022-26486
Mozilla Firefox Use-After-Free Vulnerability
8.8
CVE-2023-5217
Google Chromium libvpx Heap Buffer Overflow Vulnerability