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.

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Fixes

Solution

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Workaround

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History

Thu, 03 Sep 2026 19:15:00 +0000

Type Values Removed Values Added
CPEs cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:*

Thu, 03 Sep 2026 12:00:00 +0000

Type Values Removed Values Added
Weaknesses CWE-107
CWE-20

Thu, 03 Sep 2026 08:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Wed, 02 Sep 2026 20:30:00 +0000

Type Values Removed Values Added
Weaknesses CWE-1333
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N'}


Wed, 02 Sep 2026 01:15:00 +0000

Type Values Removed Values Added
First Time appeared Mozilla
Mozilla thunderbird
Vendors & Products Mozilla
Mozilla thunderbird

Wed, 02 Sep 2026 00:30:00 +0000

Type Values Removed Values Added
Weaknesses CWE-107
CWE-20

Tue, 01 Sep 2026 22:00:00 +0000

Type Values Removed Values Added
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.
Title Allowed UNC hostnames for attachments interpreted as a regular expression
References

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cve-icon MITRE

Status: PUBLISHED

Assigner: mozilla

Published:

Updated: 2026-09-02T19:14:29.482Z

Reserved: 2026-09-01T21:33:07.702Z

Link: CVE-2026-84642

cve-icon Vulnrichment

Updated: 2026-09-02T19:14:26.172Z

cve-icon NVD

Status : Analyzed

Published: 2026-09-01T22:17:20.000

Modified: 2026-09-03T19:00:52.377

Link: CVE-2026-84642

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-09-03T14:00:04Z

Weaknesses