The mlfi_envrcpt function in spamass-milter.cpp in SpamAssassin Milter Plugin 0.3.1, when using the expand option, allows remote attackers to execute arbitrary system commands via shell metacharacters in the RCPT TO field of an email message.
Debian Linux Security Advisory 2021-2 - spamass-milter with -x, a zombie process is left around for every mail received. This update corrects this problem.