High 7.5Published Sep 1, 2026

CVE-2026-84642Allowed UNC hostnames for attachments interpreted as a regular expression

Updated under an hour ago (2026-10-19 13:10 UTC)

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It affects Mozilla Thunderbird. Add what you run to find out whether that includes you.

No exploitation reported and no EPSS estimate yet.

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Exploited in the last 30 days

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.

CVSS: 7.5 HIGH (v3.1, CISA ADP)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Weakness (CWE): CWE-1333
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: mozilla
NVD analysis: Analyzed
Record last updated: Sep 2, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

Mozilla Thunderbird mozilla:thunderbird (from the name)	153.2 builds before 153.* not affected; from 155 not affected	CNA record
mozilla thunderbird mozilla:thunderbird	before 153.2.0; from 154.0 before 155.0	NVD

References

https://bugzilla.mozilla.org/show_bug.cgi?id=2060462permissions-required
https://www.mozilla.org/security/advisories/mfsa2026-86/vendor-advisory
https://www.mozilla.org/security/advisories/mfsa2026-88/vendor-advisory

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.