Mailpit is an email testing tool and API for developers. Prior to version 1.28.3, Mailpits SMTP server is vulnerable to Header Injection due to an insufficient Regular Expression used to validate RCPT TO and MAIL FROM addresses. An attacker can inject arbitrary SMTP headers (or corrupt existing ones) by including carriage return characters (r) in the email address. This header injection occurs because the regex intended to filter control characters fails to exclude r and n when used inside a character class. Version 1.28.3 fixes this issue.
Weakness
The product uses CRLF (carriage return line feeds) as a special element, e.g. to separate lines or records, but it does not neutralize or incorrectly neutralizes CRLF sequences from inputs.