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CVE-2026-84642

7.5 · HIGH

The values of the mail.allowed_attachment_hostnames advanced config setting were used in a regular expression without escaping.

Published Sep 1, 2026mozillaCWE-1333EPSS 0.42%

Overview

CVE-2026-84642 is a high-severity vulnerability affecting mozilla thunderbird. It was published on September 1, 2026 and has a CVSS 3.1 base score of 7.5 (HIGH).

This vulnerability has a CVSS 3.1 base score of 7.5, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

Technical 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.

Remediation

Check the references section for vendor advisories and patches from mozilla. Update thunderbird to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

Affected products

VendorProductVersionsStatus
mozillathunderbird>= 0, < 153.2.0Affected

References

Refbugzilla.mozilla.org/show_bug.cgi?id=2060462Refwww.mozilla.org/security/advisories/mfsa2026-86/Refwww.mozilla.org/security/advisories/mfsa2026-88/

How CyberStrike helps

Frequently asked questions

What is CVE-2026-84642?

CVE-2026-84642 is a high-severity vulnerability affecting mozilla thunderbird. It was published on September 1, 2026 and has a CVSS 3.1 base score of 7.5 (HIGH).

How severe is CVE-2026-84642?

This vulnerability has a CVSS 3.1 base score of 7.5, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2026-84642?

Check the references section for vendor advisories and patches from mozilla. Update thunderbird to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2026-84642?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-84642 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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