Find sigma rule 
Attack: Non-Standard Port
Adversaries may communicate using a protocol and port pairing that are typically not associated. For example, HTTPS over port 8088(Citation: Symantec Elfin Mar 2019) or port 587(Citation: Fortinet Agent Tesla April 2018) as opposed to the traditional port 443. Adversaries may make changes to the standard port used by a protocol to bypass filtering or muddle analysis/parsing of network data.
Adversaries may also make changes to victim systems to abuse non-standard ports. For example, Registry keys and other configuration settings can be used to modify protocol and port pairings.(Citation: change_rdp_port_conti)
MITRE
Tactic
- command-and-control
technique
- T1571
Test : Testing usage of uncommonly used port
OS
- linux
- macos
Description:
Testing uncommonly used port utilizing telnet.
Executor
sh