CVE-2026-84642
CVSS v3
7.5
HIGH
EPSS Score
0.4 %
exploit probability, as of 2026-09-28
CISA KEV
No
known exploited
Exploitation
—
SSVC status
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.
Technical details
- Published
- 2026-09-01
- Last Modified
- 2026-09-02
Frequently asked questions
What is CVE-2026-84642?
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.
Is CVE-2026-84642 actively exploited?
Active exploitation of CVE-2026-84642 has not been confirmed. Its EPSS score was 0.4% on 2026-09-28, the estimated probability of exploitation in the next 30 days.
What is the CVSS score for CVE-2026-84642?
CVE-2026-84642 has a CVSS v3 base score of 7.5 (HIGH severity).
Is CVE-2026-84642 affecting your environment?
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