Detection: Linux Netcat Outbound Connection

Description

The following analytic detects outbound network connections originating from Netcat or Netcat-like binaries on Linux systems. Netcat is a versatile networking utility that, while legitimate in some contexts, is frequently abused by attackers to establish reverse shells, exfiltrate data, or create persistent backdoor connections to remote systems. This activity is significant because outbound connections from these binaries often indicate an active compromise, where an attacker may be maintaining command-and-control communication or tunneling malicious traffic. If confirmed malicious, this could lead to unauthorized data exfiltration, lateral movement, or persistent remote access to the compromised system.

Search

 1
 2| tstats `security_content_summariesonly`
 3  count min(_time) as firstTime
 4        max(_time) as lastTime
 5
 6from datamodel=Network_Traffic.All_Traffic where
 7
 8All_Traffic.app IN (
 9    "*nc",
10    "*ncat",
11    "*netcat"
12)
13All_Traffic.direction="outbound"
14
15by All_Traffic.src All_Traffic.dest All_Traffic.dest_port All_Traffic.transport
16   All_Traffic.process_name All_Traffic.app All_Traffic.user All_Traffic.process_id
17
18
19| `drop_dm_object_name(All_Traffic)`
20
21| `security_content_ctime(firstTime)`
22
23| `security_content_ctime(lastTime)`
24
25| `linux_netcat_outbound_connection_filter`

Data Source

Name	Platform	Sourcetype	Source
Sysmon for Linux EventID 3	Linux	'sysmon:linux'	'Syslog:Linux-Sysmon/Operational'

Macros Used

Annotations

Default Configuration

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

Implementation

The detection is based on data that originates from Endpoint Detection and Response (EDR) agents. These agents are designed to provide security-related telemetry from the endpoints where the agent is installed. To implement this search, you must ingest logs that contain network connection events including the source, destination, port, and process context. These logs must be processed using the appropriate Splunk Technology Add-ons that are specific to the EDR product. The logs must also be mapped to the Network_Traffic data model. Use the Splunk Common Information Model (CIM) to normalize the field names and speed up the data modeling process.

Known False Positives

Legitimate system administrators or developers may use netcat for troubleshooting, port scanning, or testing network connectivity. Filter based on known administrative activity or authorized users.

Associated Analytic Story

• Linux Post-Exploitation

• Data Exfiltration

• Compromised Linux Host

• Command And Control

Intermediate Findings

Threat Objects

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