mod_sql in ProFTPD before 1.3.10rc1 allows remote attackers to execute arbitrary code via a username, in scenarios where there is logging of USER requests with an expansion such as %U, and the SQL backend allows commands (e.g., COPY TO PROGRAM).
https://zeropath.com/blog/proftpd-cve-2026-42167-auth-bypass-privesc-rce
https://github.com/proftpd/proftpd/issues/2052