{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-41319","assignerOrgId":"a0819718-46f1-4df5-94e2-005712e83aaa","state":"PUBLISHED","assignerShortName":"GitHub_M","dateReserved":"2026-04-20T14:01:46.671Z","datePublished":"2026-04-24T03:07:24.335Z","dateUpdated":"2026-04-25T01:46:35.002Z"},"containers":{"cna":{"title":"MailKit has STARTTLS Response Injection via unflushed stream buffer that enables SASL mechanism downgrade","problemTypes":[{"descriptions":[{"cweId":"CWE-74","lang":"en","description":"CWE-74: Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')","type":"CWE"}]}],"metrics":[{"cvssV3_1":{"attackComplexity":"LOW","attackVector":"NETWORK","availabilityImpact":"NONE","baseScore":6.5,"baseSeverity":"MEDIUM","confidentialityImpact":"NONE","integrityImpact":"HIGH","privilegesRequired":"NONE","scope":"UNCHANGED","userInteraction":"REQUIRED","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N","version":"3.1"}}],"references":[{"name":"https://github.com/jstedfast/MailKit/security/advisories/GHSA-9j88-vvj5-vhgr","tags":["x_refsource_CONFIRM"],"url":"https://github.com/jstedfast/MailKit/security/advisories/GHSA-9j88-vvj5-vhgr"}],"affected":[{"vendor":"jstedfast","product":"MailKit","versions":[{"version":"< 4.16.0","status":"affected"}]}],"providerMetadata":{"orgId":"a0819718-46f1-4df5-94e2-005712e83aaa","shortName":"GitHub_M","dateUpdated":"2026-04-24T03:07:24.335Z"},"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."}],"source":{"advisory":"GHSA-9j88-vvj5-vhgr","discovery":"UNKNOWN"}},"adp":[{"references":[{"url":"https://github.com/jstedfast/MailKit/security/advisories/GHSA-9j88-vvj5-vhgr","tags":["exploit"]}],"metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-04-25T01:46:14.462850Z","id":"CVE-2026-41319","options":[{"Exploitation":"poc"},{"Automatable":"no"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"title":"CISA ADP Vulnrichment","providerMetadata":{"orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","shortName":"CISA-ADP","dateUpdated":"2026-04-25T01:46:35.002Z"}}]}}