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CVE-2026-84642 Details

Description

The values of the mail.allowed_attachment_hostnames advanced config setting were used in a regular expression without escaping. For some possible valid hostnames, this could allow certain unintended hostnames to also match and serve remote attachments. This vulnerability was fixed in Thunderbird 155 and Thunderbird 153.2.

Metrics

CVSS 3.x Severity and Vector Strings:

CNA: CISA-ADPCVSS-B:7.5 HIGHVector:CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

References to Advisories, Solutions, and Tools

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URL	Source(s)	Tag(s)
https://bugzilla.mozilla.org/show_bug.cgi?id=2060462	[email protected]	Permissions Required
https://www.mozilla.org/security/advisories/mfsa2026-86/	[email protected]	Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-88/	[email protected]	Vendor Advisory

Weakness Enumeration

CWE-ID	CWE Name	Source
CWE-1333	Inefficient Regular Expression Complexity	CISA-ADP

Affected Products

Product	Versions
mozilla thunderbird	< 153.2.0 >= 154.0, < 155.0
CPE cpe:2.3:a:mozilla:thunderbird:::::::: Remediation No remediation found in references.

Change History

3 change records found show changes

Date	Action	Recorded By
Sep 3, 2026	Initial Analysis	[email protected]
Sep 2, 2026	CVE Modified	CISA-ADP
Sep 1, 2026	New CVE Received	[email protected]