What’s Vulnerable › Vulnerabilities
CVE-2026-30227: MimeKit: CRLF Injection in Quoted Local-Part Enables SMTP Command Injection and Email Forgery
- Severity: medium (CVSS 5.3 v3.1)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 1.1% probability of exploitation in the next 30 days
- Public exploit or detection template: yes
- Published: 2026-03-06 · updated 2026-06-17
- Weakness: CWE-93
Description
MimeKit is a C# library which may be used for the creation and parsing of messages using the Multipurpose Internet Mail Extension (MIME), as defined by numerous IETF specifications. Prior to version 4.15.1, a CRLF injection vulnerability in MimeKit allows an attacker to embed \r\n into the SMTP envelope address local-part (when the local-part is a quoted-string). This is non-compliant with RFC 5321 and can result in SMTP command injection (e.g., injecting additional RCPT TO / DATA / RSET commands) and/or mail header injection, depending on how the application uses MailKit/MimeKit to construct and send messages. The issue becomes exploitable when the attacker can influence a MailboxAddress (MAIL FROM / RCPT TO) value that is later serialized to an SMTP session. RFC 5321 explicitly defines the SMTP mailbox local-part grammar and does not permit CR (13) or LF (10) inside Quoted-string (qtextSMTP and quoted-pairSMTP ranges exclude control characters). SMTP commands are terminated by <CRLF>, making CRLF injection in command arguments particularly dangerous. This issue has been patched in version 4.15.1.
Affected products
- jstedfast MimeKit: before 4.15.1 — fixed in 4.15.1
How to fix
Upgrade to a fixed version: jstedfast MimeKit 4.15.1. Check the vendor advisory for mitigations.
References
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