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. 
Web Protocols
source_name: mitre-attack  url: https://attack.mitre.org/techniques/T1071/001  external_id: T1071.001     source_name: CrowdStrike Putter Panda  description: Crowdstrike Global Intelligence Team. (2014, June 9). CrowdStrike Intelligence Report: Putter Panda. Retrieved January 22, 2016.  url: http://cdn0.vox-cdn.com/assets/4589853/crowdstrike-intelligence-report-putter-panda.original.pdf     source_name: University of Birmingham C2  description: Gardiner, J.,  Cova, M., Nagaraja, S. (2014, February). Command & Control Understanding, Denying and Detecting. Retrieved April 20, 2016.  url: https://arxiv.org/ftp/arxiv/papers/1408/1408.1136.pdf     source_name: Brazking-Websockets  description: Shahar Tavor. (n.d.). BrazKing Android Malware Upgraded and Targeting Brazilian Banks. Retrieved March 24, 2023.  url: https://securityintelligence.com/posts/brazking-android-malware-upgraded-targeting-brazilian-banks/     