VulnerabilityAnalyzed
CVE-2026-84642
The values of the mail.allowed_attachment_hostnames advanced config setting were used in a regular expression without escaping.
HIGH 7.5EPSS 0.25%
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (0.25%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
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.
- CVSS 3.1
- 7.5 HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
- EPSS
- 0.25% probability · 17th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-1333
- Affected
- mozilla/thunderbird
- Source
- security@mozilla.org
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
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.