Is CVE-2026-0818 in the CISA KEV catalog?

No. CVE-2026-0818 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2026-0818?

CVE-2026-0818 has a CVSS v3 base score of 4.3 (MEDIUM).

What is the EPSS score for CVE-2026-0818?

CVE-2026-0818 has an EPSS score of 0.16% (5th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2026-0818?

Upgrade thunderbird on debian 11 to 1:140.7.1esr-1~deb11u1 or later. Fixes are available for 3 affected products.

CVE & CISA-KEV Catalog

CVE-2026-0818

MEDIUM

4.3

CVSS v3

NVD

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.

CWE-116 CWE-200Information Exposure CWE-352Cross-Site Request Forgery

How to fix

Remediation Available

thunderbirdDebian

Fixed in:1:140.7.1esr-1~deb11u1CVE-2026-0818

Fixed in:1:140.7.1esr-1~deb12u1CVE-2026-0818

Fixed in:1:140.7.1esr-1~deb13u1CVE-2026-0818

Fixed in:1:140.7.1esr-1CVE-2026-0818

thunderbirdUbuntu

Fixed in:1:140.7.1+build1-0ubuntu0.22.04.1USN-7991-1

Mozilla Thunderbird (en-US)Windows application

Affected:140.7.1Fixed in:140.7.1Mozilla

Affected:147.0.1Fixed in:147.0.1Mozilla

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionRequired

ScopeUnchanged

Impact

ConfidentialityLow

IntegrityNone

AvailabilityNone

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N

Exploit Intelligence

0.16%probability of exploitation in 30 days

5thpercentile

Low risk: more likely to be exploited than 5% of all known CVEs.

References

Vendor Advisory2

Other references2

Related Vulnerabilities

Other CWE-116 vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2024-38475	Critical	9.1	100%	KEV	Fix
CVE-2022-36446	Critical	9.8	96%	-	Fix
CVE-2021-31806	Medium	6.5	96%	-	Fix
CVE-2022-30781	High	7.5	88%	-	Fix
CVE-2022-36099	Critical	9.9	76%	-	Fix
CVE-2022-36100	Critical	9.9	74%	-	Fix

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-04-13.