CVE-2026-0818
CSS-based exfiltration of the content from partially encrypted emails when allowing remote content
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.
INFO
Published Date :
Jan. 28, 2026, 8:16 a.m.
Last Modified :
Feb. 4, 2026, 10:16 a.m.
Remotely Exploit :
Yes !
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 3.1 | MEDIUM | 134c704f-9b21-4f2e-91b3-4a467353bcc0 |
Solution
- Update Thunderbird to version 147.0.1 or later.
- Update Thunderbird to version 140.7.1 or later.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-0818.
| URL | Resource |
|---|---|
| https://bugzilla.mozilla.org/show_bug.cgi?id=1881530 | Permissions 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 |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-0818 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-0818
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-0818 vulnerability anywhere in the article.
-
security.nl
Thunderbird dicht lek dat aanvaller inhoud versleutelde e-mail laat stelen
De makers van e-mailclient Thunderbird hebben een beveiligingsupdate uitgebracht wegens een kwetsbaarheid waardoor een aanvaller de inhoud van versleutelde e-mail kan stelen. De Duitse overheid stelt ... Read more
The following table lists the changes that have been made to the
CVE-2026-0818 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
CVE Modified by af854a3a-2127-422b-91ae-364da2661108
Feb. 04, 2026
Action Type Old Value New Value Added Reference https://lists.debian.org/debian-lts-announce/2026/02/msg00005.html -
CVE Modified by [email protected]
Jan. 31, 2026
Action Type Old Value New Value Changed Description CSS-based exfiltration of the content from partially encrypted emails when allowing remote content. This vulnerability affects Thunderbird < 147.0.1 and Thunderbird < 140.7.1. 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. -
Initial Analysis by [email protected]
Jan. 30, 2026
Action Type Old Value New Value Added CPE Configuration OR *cpe:2.3:a:mozilla:thunderbird:*:*:*:*:-:*:*:* versions up to (excluding) 147.0.1 *cpe:2.3:a:mozilla:thunderbird:*:*:*:*:esr:*:*:* versions up to (excluding) 140.7.1 Added Reference Type Mozilla Corporation: https://bugzilla.mozilla.org/show_bug.cgi?id=1881530 Types: Permissions Required Added Reference Type Mozilla Corporation: https://www.mozilla.org/security/advisories/mfsa2026-07/ Types: Vendor Advisory Added Reference Type Mozilla Corporation: https://www.mozilla.org/security/advisories/mfsa2026-08/ Types: Vendor Advisory -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Jan. 28, 2026
Action Type Old Value New Value Added CVSS V3.1 AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N Added CWE CWE-352 Added CWE CWE-200 Added CWE CWE-116 -
New CVE Received by [email protected]
Jan. 28, 2026
Action Type Old Value New Value Added Description CSS-based exfiltration of the content from partially encrypted emails when allowing remote content. This vulnerability affects Thunderbird < 147.0.1 and Thunderbird < 140.7.1. Added Reference https://bugzilla.mozilla.org/show_bug.cgi?id=1881530 Added Reference https://www.mozilla.org/security/advisories/mfsa2026-07/ Added Reference https://www.mozilla.org/security/advisories/mfsa2026-08/