CVE-2026-0818

Name	CVE-2026-0818
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 affects Thunderbird < 147.0.1 and Thunderbird < 140.7.1.
Source	CVE (at NVD; CERT, ENISA, LWN, oss-sec, fulldisc, Debian ELTS, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, GitHub advisories/code/issues, web search, more)
References	DLA-4466-1, DSA-6118-1

Vulnerable and fixed packages

The table below lists information on source packages.

Source Package	Release	Version	Status
thunderbird (PTS)	bullseye	1:115.12.0-1~deb11u1	vulnerable
	bullseye (security)	1:140.7.1esr-1~deb11u1	fixed
	bookworm	1:140.6.0esr-1~deb12u1	vulnerable
	bookworm (security)	1:140.7.1esr-1~deb12u1	fixed
	trixie	1:140.6.0esr-1~deb13u1	vulnerable
	trixie (security)	1:140.7.1esr-1~deb13u1	fixed
	forky, sid	1:140.7.1esr-1	fixed

The information below is based on the following data on fixed versions.

Package	Type	Release	Fixed Version	Origin
thunderbird	source	bullseye	1:140.7.1esr-1~deb11u1	DLA-4466-1
thunderbird	source	bookworm	1:140.7.1esr-1~deb12u1	DSA-6118-1
thunderbird	source	trixie	1:140.7.1esr-1~deb13u1	DSA-6118-1
thunderbird	source	(unstable)	1:140.7.1esr-1

https://www.mozilla.org/en-US/security/advisories/mfsa2026-08/#CVE-2026-0818