Cisco NVM - Suspicious Network Connection From Process With No Args
Description
This analytic detects system binaries that are commonly abused in process injection techniques but are observed without any command-line arguments.
It leverages Cisco Network Visibility Module (NVM) flow data and process arguments
to identify outbound connections initiated by curl where TLS checks were explicitly disabled.
Binaries such as rundll32.exe, regsvr32.exe, dllhost.exe, svchost.exe, and others are legitimate Windows processes that are often injected into by malware or post-exploitation frameworks (e.g., Cobalt Strike) to hide execution.
When these processes are seen initiating a network connection with an empty or missing command line, it can indicate
potential injection and communication with a command and control server.
Query · spl
`cisco_network_visibility_module_flowdata`
process_name IN (
"backgroundtaskhost.exe", "svchost.exe", "dllhost.exe", "werfault.exe",
"searchprotocolhost.exe", "wuauclt.exe", "spoolsv.exe", "rundll32.exe",
"regasm.exe", "regsvr32.exe", "regsvcs.exe"
)
NOT process_arguments="*"
NOT dest IN (
"10.0.0.0/8", "172.16.0.0/12", "192.168.0.0/16", "100.64.0.0/10",
"127.0.0.0/8", "169.254.0.0/16", "192.0.0.0/24", "192.0.0.0/29", "192.0.0.8/32",
"192.0.0.9/32", "192.0.0.10/32", "192.0.0.170/32", "192.0.0.171/32", "192.0.2.0/24",
"192.31.196.0/24", "192.52.193.0/24", "192.88.99.0/24", "224.0.0.0/4", "192.175.48.0/24",
"198.18.0.0/15", "198.51.100.0/24", "203.0.113.0/24", "240.0.0.0/4", "::1"
)
| 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___suspicious_network_connection_from_process_with_no_args_filter`
Implementation guide
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
- Some system binaries may execute without arguments in rare legitimate scenarios (e.g., certain service launches), and initiate a network connection to microsoft servers for telemetry or update purposes. Apply additional filters as needed. However, binaries such as `rundll32.exe` or `dllhost.exe` running with no command-line context are highly suspicious and warrant investigation.
Analyst notes
Known false positives: Some system binaries may execute without arguments in rare legitimate scenarios (e.g., certain service launches), and initiate
a network connection to microsoft servers for telemetry or update purposes. Apply additional filters as needed.
However, binaries such as rundll32.exe or dllhost.exe running with no command-line context are highly suspicious and warrant investigation.