Vulnerability · Published Jan 28, 2026 · Assigned by mozilla
CVE-2026-0818CSS-based exfiltration of the content from partially encrypted emails when allowing remote content
Medium 4.3
In plain English
A medium-severity information exposure in Thunderbird from Mozilla. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 7% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | thunderbird | 1:140.7.1esr-1~deb12u1 | DEBIAN-CVE-2026-0818 |
| Debian:12 | thunderbird | 1:140.7.1esr-1~deb12u1 | DSA-6118-1 |
| Debian:13 | thunderbird | 1:140.7.1esr-1~deb13u1 | DEBIAN-CVE-2026-0818 |
| Debian:13 | thunderbird | 1:140.7.1esr-1~deb13u1 | DSA-6118-1 |
| Debian:14 | thunderbird | 1:140.7.1esr-1 | DEBIAN-CVE-2026-0818 |
| Ubuntu:22.04:LTS | thunderbird | 1:140.7.1+build1-0ubuntu0.22.04.1 | UBUNTU-CVE-2026-0818 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Mozilla | Thunderbird | see references |
Weakness: CWE-200, CWE-352, CWE-116 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N