Detection: 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.

Search

 1`cisco_network_visibility_module_flowdata`
 2process_name IN (
 3  "backgroundtaskhost.exe", "svchost.exe", "dllhost.exe", "werfault.exe",
 4  "searchprotocolhost.exe", "wuauclt.exe", "spoolsv.exe", "rundll32.exe",
 5  "regasm.exe", "regsvr32.exe", "regsvcs.exe"
 6)
 7NOT process_arguments="*"
 8NOT dest IN (
 9        "10.0.0.0/8", "172.16.0.0/12", "192.168.0.0/16", "100.64.0.0/10", 
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", 
11        "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", 
12        "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", 
13        "198.18.0.0/15", "198.51.100.0/24", "203.0.113.0/24", "240.0.0.0/4", "::1"
14        )
15
16| stats count min(_time) as firstTime max(_time) as lastTime
17        values(parent_process_arguments) as parent_process_arguments
18        values(process_arguments) as process_arguments
19        values(parent_process_hash) as parent_process_hash
20        values(process_hash) as process_hash
21        values(module_name_list) as module_name_list
22        values(module_hash_list) as module_hash_list
23        values(dest_port) as dest_port
24        values(aliul) as additional_logged_in_users_list
25        values(dest_hostname) as dest_hostname
26        by src dest parent_process_path parent_process_integrity_level process_path process_name process_integrity_level process_id transport
27
28| `security_content_ctime(firstTime)`
29
30| `security_content_ctime(lastTime)`
31
32| table
33  parent_process_integrity_level parent_process_path parent_process_arguments parent_process_hash
34  process_integrity_level process_path process_name process_arguments process_hash process_id
35  additional_logged_in_users_list module_name_list module_hash_list
36  src dest_hostname dest dest_port transport firstTime lastTime
37
38| `cisco_nvm___suspicious_network_connection_from_process_with_no_args_filter`

Data Source

Name	Platform	Sourcetype	Source
Cisco Network Visibility Module Flow Data	Network	'cisco:nvm:flowdata'	'not_applicable'

Macros Used

Annotations

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Implementation

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.

Associated Analytic Story

• Cisco Network Visibility Module Analytics

Risk Based Analytics (RBA)

Risk Message:

The $process_name$ was seen on host $src$ executing without any command-line arguments and initiating a network connection towards $dest$. This might indicate a potential communication with a C&C server.

References

• https://redcanary.com/threat-detection-report/techniques/process-injection/

Detection Testing

Replay any dataset to Splunk Enterprise by using our replay.py tool or the UI. Alternatively you can replay a dataset into a Splunk Attack Range

Source: GitHub | Version: 1