LoFP LoFP / `rundll32.exe` using `mshtml.dll` is rare in legitimate environments. however, edge cases might exist. tuning may be needed in environments with custom automation scripts.

Techniques

Sample rules

Cisco NVM - Rundll32 Abuse of MSHTML.DLL for Payload Download

Description

This analytic detects suspicious use of rundll32.exe in combination with mshtml.dll and the export RunHTMLApplication. This behavior is often observed in malware to execute JavaScript or VBScript in memory, enabling payload staging or bypassing script execution policies and bypassing the usage of the “mshta.exe” binary. The detection leverages Cisco Network Visibility Module telemetry which offers network flow activity along with process information such as command-line arguments If confirmed malicious, this activity may indicate initial access or payload download.

Detection logic

`cisco_network_visibility_module_flowdata`
process_name = "rundll32.exe"
process_arguments = "*mshtml*"
process_arguments IN ("*135*", "*RunHTMLApplication*")

| stats count min(_time) as firstTime max(_time) as lastTime
        values(parent_process_arguments) as parent_process_arguments
        values(process_arguments) as process_arguments
        values(parent_process_hash) as parent_process_hash
        values(process_hash) as process_hash
        values(module_name_list) as module_name_list
        values(module_hash_list) as module_hash_list
        values(dest_port) as dest_port
        values(aliul) as additional_logged_in_users_list
        values(dest_hostname) as dest_hostname
        by src dest parent_process_path parent_process_integrity_level process_path process_name process_integrity_level process_id transport

| `security_content_ctime(firstTime)`

| `security_content_ctime(lastTime)`

| table
  parent_process_integrity_level parent_process_path parent_process_arguments parent_process_hash
  process_integrity_level process_path process_name process_arguments process_hash process_id
  additional_logged_in_users_list module_name_list module_hash_list
  src dest_hostname dest dest_port transport firstTime lastTime

| `cisco_nvm___rundll32_abuse_of_mshtml_dll_for_payload_download_filter`