CVE-2026-84642 — Allowed UNC hostnames for attachments interpreted as a regular expression
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 all…
Published: 2026-09-01 · CVSS: 7.5 · CVSS 3.1
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.
Source: CVE Program · Revision 8b16575c39f1e1810c5e863010da073d2d3285e7