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Mallory
Medium

Thunderbird OpenPGP inline decryption CSS-based content exfiltration

IdentifiersCVE-2026-0818CWE-200· Exposure of Sensitive Information…

When a user explicitly requests Thunderbird to decrypt an inline OpenPGP message embedded within a text section of an email that is formatted/styled with HTML/CSS, Thunderbird renders the decrypted plaintext in a context where the outer message’s CSS remains active. If the user also allows loading of remote content referenced by the outer email, an attacker can craft the email (using CSS rules plus fonts/animations) to exfiltrate the decrypted secret content. Affected versions: Thunderbird < 147.0.1 and Thunderbird < 140.7.1.

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ANALYST BRIEF

Impact, mitigation & remediation

What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.

Impact

What an attacker gets, and what they’ve been doing with it.

Information disclosure/exfiltration of decrypted email content from partially encrypted messages via CSS-based techniques when remote content is permitted.

Mitigation

If you can’t patch tonight, do this now.

Disable or restrict loading of remote content in emails (e.g., block remote images/content) to reduce exposure until patched.

Remediation

Patch, then assume compromise.

Upgrade to a fixed Thunderbird release: 147.0.1 or later, or 140.7.1 or later (as applicable to the deployed release track). On Debian, apply DSA-6118-1 fixed packages (e.g., 1:140.7.1esr-1~deb12u1 for Debian 12; 1:140.7.1esr-1~deb13u1 for Debian 13).
PUBLIC EXPLOITS

Exploits

No public exploits tracked yet. Mallory keeps watching.

VALID 0 / 0 TOTALView more in app

No public exploit code observed for this vulnerability.

EXPOSURE SURFACE

Affected products & vendors

Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.

VendorProductType
MozillaThunderbirdapplication

Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.

What this page doesn’t show

The version that knows your environment.

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Exposure mapping

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Threat actor evidence

Every observed campaign linking this CVE to a named adversary.

Associated malware

Malware families riding this exploit, with evidence and IOCs.

Detection signatures

YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.

Vendor-by-vendor mapping

Cross-references every affected SKU, including bundled OEM variants.

Social activity4

Community discussion across Reddit, Mastodon, and other social sources.