A privilege escalation vulnerability in ZOOM Call Recording 6.3.1 allows its user account (i.e., the account under which the program runs - by default, the callrec account) to elevate privileges to root by abusing the callrec-rs@.service. The callrec-rs@.service starts the /opt/callrec/bin/rs binary with root privileges, and this binary is owned by callrec. It can be replaced by a Trojan horse.