rssh version 2.3.4 contains a CWE-77: Improper Neutralization of Special Elements used in a Command ('Command Injection') vulnerability in allowscp permission that can result in Local command execution. This attack appear to be exploitable via An authorized SSH user with the allowscp permission.
https://www.debian.org/security/2019/dsa-4377
https://usn.ubuntu.com/3946-1/
https://security.gentoo.org/glsa/202007-29
https://lists.debian.org/debian-lts-announce/2019/01/msg00027.html
https://esnet-security.github.io/vulnerabilities/20190115_rssh