High severity7.5NVD Advisory· Published Sep 1, 2026· Updated Sep 3, 2026
CVE-2026-84642
CVE-2026-84642
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.
Affected products
2- Range: <=153.2, <155
Patches
Vulnerability mechanics
References
3- www.mozilla.org/security/advisories/mfsa2026-86/nvdVendor Advisory
- www.mozilla.org/security/advisories/mfsa2026-88/nvdVendor Advisory
- bugzilla.mozilla.org/show_bug.cginvdPermissions Required
News mentions
1- Mozilla Thunderbird: 16 Vulnerabilities Including Critical Sandbox Escapes Disclosed TogetherVypr Intelligence · Sep 1, 2026