Find sigma rule 
Attack: Application Layer Protocol: Web Protocols
Adversaries may communicate using application layer protocols associated with web traffic to avoid detection/network filtering by blending in with existing traffic. Commands to the remote system, and often the results of those commands, will be embedded within the protocol traffic between the client and server.
Protocols such as HTTP/S(Citation: CrowdStrike Putter Panda) and WebSocket(Citation: Brazking-Websockets) that carry web traffic may be very common in environments. HTTP/S packets have many fields and headers in which data can be concealed. An adversary may abuse these protocols to communicate with systems under their control within a victim network while also mimicking normal, expected traffic.
MITRE
Tactic
- command-and-control
technique
- T1071.001
Test : Malicious User Agents - Powershell
OS
- windows
Description:
This test simulates an infected host beaconing to command and control. Upon execution, no output will be displayed. Use an application such as Wireshark to record the session and observe user agent strings and responses.
Inspired by APTSimulator - https://github.com/NextronSystems/APTSimulator/blob/master/test-sets/command-and-control/malicious-user-agents.bat
Executor
powershell
Sigma Rule
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proc_creation_win_susp_web_request_cmd_and_cmdlets.yml (id: 9fc51a3c-81b3-4fa7-b35f-7c02cf10fd2d)
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posh_ps_susp_invoke_webrequest_useragent.yml (id: d4488827-73af-4f8d-9244-7b7662ef046e)
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posh_ps_web_request_cmd_and_cmdlets.yml (id: 1139d2e2-84b1-4226-b445-354492eba8ba)
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net_connection_win_powershell_network_connection.yml (id: 1f21ec3f-810d-4b0e-8045-322202e22b4b)