CVE-2026-0818 — CSS-based exfiltration of the content from partially encrypted emails when allowing remote content

Affected: Mozilla Thunderbird

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.

USN-7991-1 — thunderbird vulnerabilities

Affected: Ubuntu:22.04:LTS: thunderbird

Multiple security issues were discovered in Thunderbird. If a user were tricked into opening a specially crafted website in a browsing context, an attacker could potentially exploit these to cause a denial of service, obtain sensitive information, bypass security restrictions, cross-site tracing, or execute arbitrary code.

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CVE-2026-0818 — CSS-based exfiltration of the content from partially encrypted emails when allowing remote content

USN-7991-1 — thunderbird vulnerabilities