Vulnerability record · CVE-2026-84637 · published 1 September 2026

CVE-2026-84637: Mozilla thunderbird unrestricted file upload vulnerability

Mozilla · Thunderbird

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.

9.8 CVSS 3.1 Critical EPSS 0.63% · top 52.1% CWE-434 · Unrestricted file upload

9.8CVSS 3.1 base score

0.63%EPSS exploitation probability, 30 days

NoNot in CISA KEV

1Affected product versions listed by NVD

3References

3 Sep 2026Last modified by NVD

Description

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

Thunderbird Mozilla

References

Link	Tags
https://bugzilla.mozilla.org/show_bug.cgi?id=2043878	Permissions Required
https://www.mozilla.org/security/advisories/mfsa2026-78/	Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-88/	Vendor Advisory

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Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2026-84637), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.