CVE-2026-84642CWE-1333

CVE-2026-84642

High · published September 2, 2026

CVSS v3.1
7.5
EPSS
0%
Percentile
16.8
In the wild
Unconfirmed
What it is

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.

The record
Technical detail
CVSS v3.1
7.5 · HIGH
Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
CVSS v4.0
Not supplied
EPSS
0.00254 · 16.8th percentile
Weakness
CWE-1333 · Inefficient Regular Expression Complexity
Published
2026-09-02T02:17Z
Affected products (2)
ProductVersionsFixed in
mozilla/thunderbird< 153.2.0153.2.0
mozilla/thunderbird≥ 154.0, < 155.0155.0
References (3)
https://bugzilla.mozilla.org/show_bug.cgi?id=2060462 · [email protected]https://www.mozilla.org/security/advisories/mfsa2026-86/ · [email protected]https://www.mozilla.org/security/advisories/mfsa2026-88/ · [email protected]
EPSS history
Timeline
  • 03 SEP 03:32Z
    EPSS moved — → 0%
    epss
  • 01 SEP 21:33Z
    Allowed UNC hostnames for attachments interpreted as a regular expression
    cvelistv5