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

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Summary

CVECVE-2026-0818
StatePUBLISHED
Assignermozilla
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-01-28 08:16:03 UTC
Updated2026-04-13 15:17:15 UTC
DescriptionWhen 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.

Risk And Classification

Primary CVSS: v3.1 4.3 MEDIUM from ADP

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

EPSS: 0.000070000 probability, percentile 0.005060000 (date 2026-04-15)

Problem Types: CWE-116 | CWE-200 | CWE-352 | CWE-200 CWE-200 Exposure of Sensitive Information to an Unauthorized Actor | CWE-352 CWE-352 Cross-Site Request Forgery (CSRF) | CWE-116 CWE-116 Improper Encoding or Escaping of Output

VersionSourceTypeScoreSeverityVector
3.1ADPDECLARED4.3MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N
3.1134c704f-9b21-4f2e-91b3-4a467353bcc0Secondary4.3MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
Required
Scope
Unchanged
Confidentiality
Low
Integrity
None
Availability
None

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

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Application Mozilla Thunderbird All All All All
Application Mozilla Thunderbird All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Mozilla Thunderbird unaffected 140.7.1 140.* rpm Not specified
CNA Mozilla Thunderbird unaffected 147.0.1 * rpm Not specified

References

ReferenceSourceLinkTags
www.mozilla.org/security/advisories/mfsa2026-08 [email protected] www.mozilla.org Vendor Advisory
www.mozilla.org/security/advisories/mfsa2026-07 [email protected] www.mozilla.org Vendor Advisory
bugzilla.mozilla.org/show_bug.cgi [email protected] bugzilla.mozilla.org Permissions Required
lists.debian.org/debian-lts-announce/2026/02/msg00005.html af854a3a-2127-422b-91ae-364da2661108 lists.debian.org
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: Leon Trampert, Daniel Weber, Christian Rossow, Michael Schwarz (en)

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