Bug 2433720 (CVE-2026-0818)

Summary: CVE-2026-0818 thunderbird: CSS-based exfiltration of the content from partially encrypted emails when allowing remote content
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: unspecified Docs Contact:
Priority: unspecified    
Version: unspecifiedCC: gotiwari, jgrulich, jhorak, mvyas, tpopela
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in Thunderbird. The Mozilla Foundation's Security Advisory describes the following issue: 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.
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Description OSIDB Bzimport 2026-01-28 08:01:28 UTC
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.