CVE-2026-0818

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{"bugzilla": {"description": "thunderbird: CSS-based exfiltration of the content from partially encrypted emails when allowing remote content", "id": "2433720", "url": "https://bugzilla.redhat.com/show_bug.cgi?id=2433720"}, "csaw": false, "cvss3": {"cvss3_base_score": "6.1", "cvss3_scoring_vector": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N", "status": "draft"}, "details": ["No description is available for this CVE."], "name": "CVE-2026-0818", "package_state": [{"cpe": "cpe:/o:redhat:enterprise_linux:10", "fix_state": "Not affected", "package_name": "rhel10/thunderbird-flatpak", "product_name": "Red Hat Enterprise Linux 10"}, {"cpe": "cpe:/o:redhat:enterprise_linux:10", "fix_state": "Not affected", "package_name": "thunderbird", "product_name": "Red Hat Enterprise Linux 10"}, {"cpe": "cpe:/o:redhat:enterprise_linux:6", "fix_state": "Not affected", "package_name": "thunderbird", "product_name": "Red Hat Enterprise Linux 6"}, {"cpe": "cpe:/o:redhat:enterprise_linux:7", "fix_state": "Not affected", "package_name": "thunderbird", "product_name": "Red Hat Enterprise Linux 7"}, {"cpe": "cpe:/o:redhat:enterprise_linux:8", "fix_state": "Not affected", "package_name": "thunderbird", "product_name": "Red Hat Enterprise Linux 8"}, {"cpe": "cpe:/o:redhat:enterprise_linux:9", "fix_state": "Not affected", "package_name": "thunderbird", "product_name": "Red Hat Enterprise Linux 9"}], "public_date": "2026-01-28T07:39:17Z", "references": ["https://www.cve.org/CVERecord?id=CVE-2026-0818\nhttps://nvd.nist.gov/vuln/detail/CVE-2026-0818\nhttps://www.mozilla.org/security/advisories/mfsa2026-07/#CVE-2026-0818"], "statement": "ed Hat Product Security rates the severity of this flaw as determined by the Mozilla Foundation Security Advisory."}

{"analysis": {"en": {"generated_at": "2026-04-15T15:50:51.803458+00:00", "value": {"mitigation_remediation": ["Upgrade Thunderbird to version 147.0.1 or newer, or Thunderbird ESR 140.7.1 or newer, which includes the patch for this vulnerability.", "Configure Thunderbird to block remote content when viewing encrypted messages by disabling the 'Allow loading of remote content' setting in the account or global preferences.", "Avoid automatically decrypting OpenPGP messages in emails that contain HTML content; instead decrypt manually after verifying the sender\u2019s identity."], "summary": {"action": "Apply Patch", "impact": "Information Disclosure via CSS-based Exfiltration"}, "threat_synthesis": {"affected_systems": "All versions of Mozilla Thunderbird before 147.0.1 and, for the ESR channel, before 140.7.1 are affected. The issue is present in builds that support OpenPGP decryption and HTML email rendering and is resolved in the referenced release numbers.", "description_and_impact": "When a user explicitly decrypts an inline OpenPGP message that is embedded within an HTML\u2011styled email, the decrypted content is rendered inside the same CSS context as the outer message. An attacker can craft CSS rules, custom fonts, and animations that expose the hidden plaintext or coerce the client to transmit it to a remote endpoint, enabling the confidential contents of the email to be exfiltrated. This flaw results in an information\u2011disclosure vulnerability.", "risk_and_exploitability": "The exploit requires the user to both decrypt the message and have the remote content option enabled, making it a user\u2011interaction attack. The CVSS score of 4.3 reflects its moderate severity given these prerequisites. End users are unlikely to encounter widespread exploitation, and the EPSS score of less than 1% indicates a low likelihood of attack. The flaw is not listed in the KEV catalog, suggesting it has not yet been actively exploited at scale. Nevertheless, the vulnerability should be mitigated promptly to prevent potential information leaks."}}}}, "created": "2026-01-29T09:18:26.239629+00:00", "updated": "2026-04-15T18:00:15.531316+00:00", "vendors": ["mozilla", "mozilla$PRODUCT$thunderbird"]}