CVE-2026-84637CWE-434unrestricted-file-upload

CVE-2026-84637

Critical · published September 2, 2026

CVSS v3.1
9.8
EPSS
1%
Percentile
49.3
In the wild
Unconfirmed
What it is

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.

The record
Technical detail
CVSS v3.1
9.8 · CRITICAL
Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CVSS v4.0
Not supplied
EPSS
0.00626 · 49.3th percentile
Weakness
CWE-434 · Unrestricted Upload of File with Dangerous Type
Published
2026-09-02T02:17Z
Affected products (2)
ProductVersionsFixed in
mozilla/thunderbird< 153.2.0153.2.0
mozilla/thunderbird≥ 154.0, < 155.0155.0
References (3)
https://bugzilla.mozilla.org/show_bug.cgi?id=2043878 · [email protected]https://www.mozilla.org/security/advisories/mfsa2026-78/ · [email protected]https://www.mozilla.org/security/advisories/mfsa2026-88/ · [email protected]
EPSS history
Timeline
  • 03 SEP 03:32Z
    EPSS moved — → 0%
    epss
  • 01 SEP 21:25Z
    Calendar invitation attachments could launch local executables
    cvelistv5