{"id":"CVE-2026-41319","revision":"237a42eedd9b44e7b86e4d98ef17ff41","records":[{"revision":"237a42eedd9b44e7b86e4d98ef17ff41","observedAt":"2026-10-23T15:48:27.903+00:00","statement":{"source":"cve-program","id":"CVE-2026-41319","aliases":[],"title":"MailKit has STARTTLS Response Injection via unflushed stream buffer that enables SASL mechanism downgrade","description":"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.","state":0,"publishedAt":"2026-04-24T03:07:24.335+00:00","modifiedAt":"2026-04-25T01:46:35.002+00:00","affected":[{"ecosystem":"Vendor product","name":"MailKit","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"vendor\": \"jstedfast\",\n                    \"product\": \"MailKit\",\n                    \"versions\": [\n                        {\n                            \"version\": \"< 4.16.0\",\n                            \"status\": \"affected\"\n                        }\n                    ]\n                }"}],"metrics":[{"system":"CVSS 3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N","score":6.5,"severity":"MEDIUM"}],"references":["https://github.com/jstedfast/MailKit/security/advisories/GHSA-9j88-vvj5-vhgr"],"sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-41319","license":"CVE Program Terms of Use","key":"cve-program:CVE-2026-41319","identifiers":["CVE-2026-41319"]},"retained":false,"historicalAffected":[]}],"coverage":[]}