Name:Cisco NVM - Rundll32 Abuse of MSHTML.DLL for Payload Download id:18f0d27d-569e-4bc4-96e1-09b214fa73c0 version:1 date:2025-07-03 author:Nasreddine Bencherchali, Splunk status:production type:Anomaly 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.
Data_source:
-Cisco Network Visibility Module Flow Data
search:`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`
how_to_implement:This search requires Network Visibility Module logs, which includes the flow data sourcetype.
This search uses an input macro named `cisco_network_visibility_module_flowdata`.
We strongly recommend that you specify your environment-specific configurations
(index, source, sourcetype, etc.) for Cisco Network Visibility Module logs.
Replace the macro definition with configurations for your Splunk environment.
The search also uses a post-filter macro designed to filter out known false positives.
The logs are to be ingested using the Splunk Add-on for Cisco Endpoint Security Analytics (CESA) (https://splunkbase.splunk.com/app/4221).
known_false_positives:`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.
References: -https://lolbas-project.github.io/lolbas/Binaries/Rundll32/ -https://redcanary.com/blog/threat-detection/threat-research-questions/ -https://twitter.com/n1nj4sec/status/1421190238081277959 -https://hyp3rlinx.altervista.org/advisories/MICROSOFT_WINDOWS_DEFENDER_TROJAN.WIN32.POWESSERE.G_MITIGATION_BYPASS_PART2.txt -http://hyp3rlinx.altervista.org/advisories/MICROSOFT_WINDOWS_DEFENDER_DETECTION_BYPASS.txt drilldown_searches: name:'View the detection results for - "$src$"' search:'%original_detection_search% | search src = "$src$"' earliest_offset:'$info_min_time$' latest_offset:'$info_max_time$' name:'View risk events for the last 7 days for - "$src$"' search:'| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$src$") starthoursago=168 | stats count min(_time) as firstTime max(_time) as lastTime values(search_name) as "Search Name" values(risk_message) as "Risk Message" values(analyticstories) as "Analytic Stories" values(annotations._all) as "Annotations" values(annotations.mitre_attack.mitre_tactic) as "ATT&CK Tactics" by normalized_risk_object | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)`' earliest_offset:'$info_min_time$' latest_offset:'$info_max_time$' tags: analytic_story: - 'Cisco Network Visibility Module Analytics' asset_type:Endpoint mitre_attack_id: - 'T1218.005' product: - 'Splunk Enterprise' - 'Splunk Enterprise Security' security_domain:endpoint
