Unintended remote attachment loads via unescaped hostname regex
Published Sep 1, 2026 · Updated Sep 2, 2026
Improper hostname validation in Mozilla Thunderbird before 155 or 153.2 allows remote attackers to serve unintended remote attachments. The mail.allowed_attachment_hostnames setting inserts configured hostnames into a regular expression without escaping metacharacters, so the pattern accepts additional hostnames. Exploitation requires a configured allowed hostname with regex metacharacters and an attacker-controlled hostname that matches the expanded pattern.
Summary
What happened
Improper hostname validation in Mozilla Thunderbird before 155 or 153.2 allows remote attackers to serve unintended remote attachments. The mail.allowed_attachment_hostnames setting inserts configured hostnames into a regular expression without escaping metacharacters, so the pattern accepts additional hostnames. Exploitation requires a configured allowed hostname with regex metacharacters and an attacker-controlled hostname that matches the expanded pattern.
The record
- CVE
- CVE-2026-84642
- Published
- Sep 1, 2026
- Updated
- Sep 2, 2026
- Vendor
- Unknown vendor
- Product
- Unknown product
- Classifications
- CWE-1333
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Sep 1, 2026CVE publishedPublication date reported by the CVE source.
- Sep 2, 2026Record updatedLatest update available in the CVE record.
Exploitability
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Published CVSS scores
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Attacks
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Technologies
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