Advisories for Cargo/Lettre package

An inverted-boolean bug in lettre's boring-tls integration silently disables TLS hostname verification for callers using the default (strict) configuration. An on-path attacker presenting any chain-valid certificate for any domain can intercept SMTP submission, including PLAIN/LOGIN credentials and message contents, against any lettre user built with the boring-tls feature. Other TLS backends (native-tls, rustls) are unaffected.

Affected versions of lettre allowed argument injection to the sendmail command. It was possible, using forged to addresses, to pass arbitrary arguments to the sendmail executable. Depending on the implementation (original sendmail, postfix, exim, etc.) it could be possible in some cases to write email data into abritrary files (using sendmail's logging features). NOTE: This vulnerability only affects the sendmail transport. Others, including smtp, are not affected.

Affected versions of lettre allowed SMTP command injection through an attacker's controlled message body. The module for escaping lines starting with a period wouldn't catch a period that was placed after a double CRLF sequence, allowing the attacker to end the current message and write arbitrary SMTP commands after it.