Improper Handling of Exceptional Conditions
smtp_mailaddr in smtp_session.c in OpenSMTPD 6.6, as used in OpenBSD 6.6 and other products, allows remote attackers to execute arbitrary commands as root via a crafted SMTP session, as demonstrated by shell metacharacters in a MAIL FROM field. This affects the "uncommented" default configuration. The issue exists because of an incorrect return value upon failure of input validation.
CWE-755 - Improper Handling of Exceptional Conditions
The software does not handle or incorrectly handles an exceptional condition.