{"id":"CVE-2026-41319","sourceIdentifier":"security-advisories@github.com","published":"2026-04-24T04:16:20.400","lastModified":"2026-06-17T10:46:30.013","vulnStatus":"Analyzed","cveTags":[],"descriptions":[{"lang":"en","value":"MailKit is a cross-platform mail client library built on top of MimeKit. A STARTTLS Response Injection vulnerability in versions prior to 4.16.0 allows a Man-in-the-Middle attacker to inject arbitrary protocol responses across the plaintext-to-TLS trust boundary, enabling SASL authentication mechanism downgrade (e.g., forcing PLAIN instead of SCRAM-SHA-256). The internal read buffer in `SmtpStream`, `ImapStream`, and `Pop3Stream` is not flushed when the underlying stream is replaced with `SslStream` during STARTTLS upgrade, causing pre-TLS attacker-injected data to be processed as trusted post-TLS responses. Version 4.16.0 patches the issue."}],"affected":[{"source":"security-advisories@github.com","affectedData":[{"vendor":"jstedfast","product":"MailKit","versions":[{"version":"< 4.16.0","status":"affected"}]}]}],"metrics":{"cvssMetricV31":[{"source":"security-advisories@github.com","type":"Secondary","cvssData":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N","baseScore":6.5,"baseSeverity":"MEDIUM","attackVector":"NETWORK","attackComplexity":"LOW","privilegesRequired":"NONE","userInteraction":"REQUIRED","scope":"UNCHANGED","confidentialityImpact":"NONE","integrityImpact":"HIGH","availabilityImpact":"NONE"},"exploitabilityScore":2.8,"impactScore":3.6},{"source":"nvd@nist.gov","type":"Primary","cvssData":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N","baseScore":5.9,"baseSeverity":"MEDIUM","attackVector":"NETWORK","attackComplexity":"HIGH","privilegesRequired":"NONE","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"NONE","integrityImpact":"HIGH","availabilityImpact":"NONE"},"exploitabilityScore":2.2,"impactScore":3.6}],"ssvcV203":[{"source":"134c704f-9b21-4f2e-91b3-4a467353bcc0","ssvcData":{"timestamp":"2026-04-25T01:46:14.462850Z","id":"CVE-2026-41319","options":[{"exploitation":"poc"},{"automatable":"no"},{"technicalImpact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}]},"weaknesses":[{"source":"security-advisories@github.com","type":"Secondary","description":[{"lang":"en","value":"CWE-74"}]}],"configurations":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:a:jstedfast:mailkit:*:*:*:*:*:*:*:*","versionEndExcluding":"4.16.0","matchCriteriaId":"93C4C88D-7A8F-468C-90DE-0BBD8B916D6A"}]}]}],"references":[{"url":"https://github.com/jstedfast/MailKit/security/advisories/GHSA-9j88-vvj5-vhgr","source":"security-advisories@github.com","tags":["Exploit","Vendor Advisory"]},{"url":"https://github.com/jstedfast/MailKit/security/advisories/GHSA-9j88-vvj5-vhgr","source":"134c704f-9b21-4f2e-91b3-4a467353bcc0","tags":["Exploit","Vendor Advisory"]}]}