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CVE-2026-0818

4.3 · MEDIUM

When a user explicitly requested Thunderbird to decrypt an inline OpenPGP message that was embedded in a text section of an email that was formatted and styled with HTML and CSS, then the decrypted…

Published Jan 28, 2026CWE-116EPSS 0.18%

Overview

CVE-2026-0818 is a medium-severity vulnerability. It was published on January 28, 2026 and has a CVSS 3.1 base score of 4.3 (MEDIUM).

This vulnerability has a CVSS 3.1 base score of 4.3, rated MEDIUM. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

Technical description

When a user explicitly requested Thunderbird to decrypt an inline OpenPGP message that was embedded in a text section of an email that was formatted and styled with HTML and CSS, then the decrypted contents were rendered in a context in which the CSS styles from the outer messages were active. If the user had additionally allowed loading of the remote content referenced by the outer email message, and the email was crafted by the sender using a combination of CSS rules and fonts and animations, then it was possible to extract the secret contents of the email. This vulnerability was fixed in Thunderbird 147.0.1 and Thunderbird 140.7.1.

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. 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.

References

Refbugzilla.mozilla.org/show_bug.cgi?id=1881530Refwww.mozilla.org/security/advisories/mfsa2026-07/Refwww.mozilla.org/security/advisories/mfsa2026-08/Reflists.debian.org/debian-lts-announce/2026/02/msg00005.html

How CyberStrike helps

Frequently asked questions

What is CVE-2026-0818?

CVE-2026-0818 is a medium-severity vulnerability. It was published on January 28, 2026 and has a CVSS 3.1 base score of 4.3 (MEDIUM).

How severe is CVE-2026-0818?

This vulnerability has a CVSS 3.1 base score of 4.3, rated MEDIUM. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2026-0818?

Check the references section for vendor advisories, patches, and mitigation guidance. 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-2026-0818?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-0818 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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