Bug#952421: Cannot use PAM modules which call subprocess e.g. pam_exec
The issue is fixed in this patch: https://src.fedoraproject.org/rpms/vsftpd/raw/main/f/0026-Prevent-hanging-in-SIGCHLD-handler.patch It applies flawlessly to the debian version of vsftpd.
Bug#952421: Cannot use PAM modules which call subprocess e.g. pam_exec
Package: vsftpd Version: version 3.0.3 Description: It seems vsftpd blocks/hang if you use a PAM module which call a subprocess like pam_exec. See this thread on StackExchange, which also claim the CentOS package have fixed the bug. https://askubuntu.com/questions/406486/vsftpd-hanging-when-using-pam-exec-or-pam-script#answer-778448