MITRE ATT&CK

Adversaries may attempt to blend in with legitimate traffic by spoofing browser and system attributes like operating system, system language, platform, user-agent string, resolution, time zone, etc. The HTTP User-Agent request header is a string that lets servers and network peers identify the application, operating system, vendor, and/or version of the requesting user agent.(Citation: Mozilla User Agent)

Adversaries may gather this information through System Information Discovery or by users navigating to adversary-controlled websites, and then use that information to craft their web traffic to evade defenses.(Citation: Gummy Browsers Targeted Browser Spoofing against State-of-the-Art Fingerprinting Techniques)