Medium 4.3Published Jan 28, 2026

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

Updated under an hour ago (Oct 26, 2026, 5:50 AM ET)

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It affects Mozilla Thunderbird. Add what you run to find out whether that includes you.

No exploitation reported and no EPSS estimate yet.

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Exploited in the last 30 days

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.

CVSS: 4.3 MEDIUM (v3.1, CISA ADP)CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N
Weakness (CWE): CWE-200, CWE-352, CWE-116
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: mozilla
NVD analysis: Modified
Record last updated: Apr 13, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

Mozilla Thunderbird mozilla:thunderbird (from the name)	140.7.1 builds before 140.* not affected; from 147.0.1 not affected	CNA record
mozilla thunderbird mozilla:thunderbird	before 140.7.1; before 147.0.1	NVD

References

https://bugzilla.mozilla.org/show_bug.cgi?id=1881530permissions-required
https://www.mozilla.org/security/advisories/mfsa2026-07/vendor-advisory
https://www.mozilla.org/security/advisories/mfsa2026-08/vendor-advisory
https://lists.debian.org/debian-lts-announce/2026/02/msg00005.html

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.