250. CastleRAT Abuses Steam Community Pages to Store C2 Addresses

Hello everyone!

Dead Drop Resolver (T1102.001) technique becomes more and more popular among adversaries. Let's look at another example - how threat actors abuse Steam Community pages.

We'll look at CastleRAT. Since August 2025, the malware leverages Steam Community pages as C2 dead drops. It means that we can hunt for suspicious resolutions of steamcommunity[.]com. Of course, you should not forget about exclusions, so here's what to exclude based on my telemetry:

event_type: "dnsreqwin"

AND

dns_rname: "steamcommunity.com"

AND NOT

proc_file_path: ("steam.exe" OR "steam" OR "kaspersky" OR "windows defender" OR "networkservice.exe" OR "svchost.exe" OR "Counter Strike" OR "McAfee" OR "eaanticheat.gameservice.exe" OR "WinProxy" OR "NetLimiter" OR "cs.exe" OR "rave.exe" OR "ScumLauncher.exe" OR "ExpressConnect" OR "steamwebhelper.exe" OR "gearupbooster" OR "ipconfig.exe" OR "steamapps" OR "cFosSpeed" OR "arc.exe" OR "UrbanVPN" OR "wmiprvse.exe" OR "PycharmProjects" OR "Screaming Frog SEO Spider" OR "docker" OR "IntelConnectivityNetworkService.exe" OR "DrWeb" OR "powertoys" OR "hl2.exe")

And yes, you may have other exclusions - it depends on your environment.

See you tomorrow!

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