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.
Conclusion & alert: CVE-2026-0818 is rated Low Risk (18.3/100): CVSS Medium severity, with low exploitation likelihood (EPSS 0.02%). Mandatory action: Low composite risk—no urgent action required; patch on your normal maintenance cycle and revisit priority if CVSS or EPSS increases.
Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.
EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).
| # | Date | Old EPSS score | New EPSS score | Delta (New - Old) |
|---|---|---|---|---|
| 1 | 2026-01-28 | — | 0.02% | — |
Full EPSS history (1 record total)
CVSS metrics for this CVE.
| Base score | Version | Severity | Vector | Exploitability | Impact | Score source |
|---|---|---|---|---|---|---|
| 4.3 | 3.1 | MEDIUM |
|
2.8 | 1.4 | 134c704f-9b21-4f2e-91b3-4a467353bcc0 |
| vendor | priority | summary | link |
|---|---|---|---|
alpine
|
— | CVE-2026-0818: 1 source package rows (thunderbird); 51 state rows across 2 repos (3.23-community, edge-community); fixed 0, open 51. | https://security.alpinelinux.org/vuln/CVE-2026-0818 |
debian
|
not yet assigned | CVE-2026-0818 not yet assigned priority: Debian including 1 source packages (thunderbird), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. | https://security-tracker.debian.org/tracker/CVE-2026-0818 |
redhat
|
— | — | https://access.redhat.com/security/cve/CVE-2026-0818 |
suse
|
medium | CVE-2026-0818 severity moderate: SUSE including 11 source package names (MozillaThunderbird-140.7.1-1.1, MozillaThunderbird-140.7.1-150200.8.254.1, …), 17 product×package rows across 5 product lines (SUSE Linux Enterprise Module for Package Hub 15 SP7, SUSE Linux Enterprise Workstation Extension 15 SP7, … (5 product lines)): Fixed 17. | https://www.suse.com/security/cve/CVE-2026-0818/ |
ubuntu
|
medium | CVE-2026-0818 medium priority: Ubuntu including 1 source packages (thunderbird), 4 status rows across 4 suites (jammy, noble, questing, upstream): not-affected 2, needs-triage 1, released 1. | https://ubuntu.com/security/CVE-2026-0818 |
| Vendor | Product | Version | Raw CPE |
|---|---|---|---|
| mozilla | thunderbird | < 140.7.1 | cpe:2.3:a:mozilla:thunderbird:*:*:*:*:esr:*:*:* |
| mozilla | thunderbird | < 147.0.1 | cpe:2.3:a:mozilla:thunderbird:*:*:*:*:-:*:*:* |
| URL | Tags |
|---|---|
| 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 |