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.
References
| Link | Resource |
|---|---|
| https://github.com/jstedfast/MailKit/security/advisories/GHSA-9j88-vvj5-vhgr | Exploit Vendor Advisory |
| https://github.com/jstedfast/MailKit/security/advisories/GHSA-9j88-vvj5-vhgr | Exploit Vendor Advisory |
Configurations
History
21 May 2026, 19:39
| Type | Values Removed | Values Added |
|---|---|---|
| CPE | cpe:2.3:a:jstedfast:mailkit:*:*:*:*:*:*:*:* | |
| First Time |
Jstedfast mailkit
Jstedfast |
21 May 2026, 18:24
| Type | Values Removed | Values Added |
|---|---|---|
| CPE | cpe:2.3:a:mimekit:mailkit:*:*:*:*:*:*:*:* | |
| References | () https://github.com/jstedfast/MailKit/security/advisories/GHSA-9j88-vvj5-vhgr - Exploit, Vendor Advisory | |
| First Time |
Mimekit
Mimekit mailkit |
25 Apr 2026, 03:16
| Type | Values Removed | Values Added |
|---|---|---|
| References | () https://github.com/jstedfast/MailKit/security/advisories/GHSA-9j88-vvj5-vhgr - |
24 Apr 2026, 04:16
| Type | Values Removed | Values Added |
|---|---|---|
| New CVE |
Information
Published : 2026-04-24 04:16
Updated : 2026-05-21 19:39
NVD link : CVE-2026-41319
Mitre link : CVE-2026-41319
CVE.ORG link : CVE-2026-41319
JSON object : View
Products Affected
jstedfast
- mailkit
CWE
CWE-74
Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')