CVE-2026-84642

UNKNOWN 0.0

Allowed UNC hostnames for attachments interpreted as a regular expression

CVSS Score

0.0

EPSS Score

0.0%

EPSS Percentile

0th

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.

Vendor	mozilla
Product	thunderbird
Ecosystems	Browser JavaScript
Industries	Technology
Published	Sep 1, 2026
Last Updated	Sep 1, 2026

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Affected Versions

Mozilla / Thunderbird

All versions affected

References

NVD ↗ CVE.org ↗ EPSS Data ↗

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

Credits

ChinhNguyen, Lowk3yz