Linux auditd: Network service enumeration via telnet, nmap, or netcat

Alerts when telnet/nmap/netcat-style binaries are executed on Linux via auditd, consistent with service discovery scanning.

FreeReviewedSigma · Low · v3

Product: linux
Service: auditd
Author: Alejandro Ortuno, oscd.community (SigmaHQ), DRL 1.1
Published: 2020-10-21
Updated: 2026-07-31

Analysis Detection

ATT&CK techniques

Discovery

Recon
Resource Dev
Initial Access
Execution
Persistence
Priv Esc
Defense Evasion
Cred Access
Discovery
- T1046Network Service Discovery
Lateral Movement
Collection
C2
Exfiltration
Impact

What it detects

This rule flags Linux auditd syscall events where the executing binary ends with telnet, nmap, netcat, nc, ncat, or nc.openbsd. Such tools are commonly used to enumerate local or remote network services, which can precede broader discovery and access attempts. Detection relies on auditd telemetry capturing SYSCALL events with the process executable path suffix.

Reporting behind it

Related detections9 linkedT1046 — drag to rearrange

Possible Out-Of-Band Interaction via requestrepo via DNS (via dns_query)

Possible Interactsh Out-Of-Band Interaction via DNS (via dns_query)

Suspicious Advanced IP Scanner Execution for Network Discovery

Suspicious masscan Scanning Docker API Port 2375

Suspicious Network Reconnaissance via Advanced Port Scanner

Suspicious Nmap Scanner Probe URIs in HTTP Requests (via webserver)

Suspicious Internet Scanning for Docker and Kubelet Ports via masscan

Suspicious Fscan Internal Network Scanner Execution (via process_creation)

Possible Network Service Scanning via Nmap or Masscan (via process_creation)

Linux auditd: Network service enumeration via telnet, nmap, or netcat

Pivot detection · T1046 · 9 related

Changelog

v3
Candidate ingested via manual entry.2026-07-31
v2
Candidate ingested via manual entry.2026-07-31
v1
No changelog recorded for this version.2026-07-30

Detection content is published as a reviewed draft. Tune thresholds and exclusions against your own telemetry before enabling this rule for alerting.

linux-auditd-process-executions-of-telnet-nmap-netcat-for-network-service-scanni-3761e026

title: "Linux auditd: Network service enumeration via telnet, nmap, or netcat"
id: d4d3414e-f718-4e8e-9419-ceaf7672f310
related:
  - id: 3e102cd9-a70d-4a7a-9508-403963092f31
    type: derived
  - id: 3761e026-f259-44e6-8826-719ed8079408
    type: derived
status: test
description: This rule flags Linux auditd syscall events where the executing binary ends with telnet, nmap, netcat, nc, ncat, or nc.openbsd. Such tools are commonly used to enumerate local or remote network services, which can precede broader discovery and access attempts. Detection relies on auditd telemetry capturing SYSCALL events with the process executable path suffix.
references:
  - https://github.com/redcanaryco/atomic-red-team/blob/f339e7da7d05f6057fdfcdd3742bfcf365fee2a9/atomics/T1046/T1046.md
  - https://github.com/SigmaHQ/sigma/blob/master/rules/linux/auditd/syscall/lnx_auditd_network_service_scanning.yml
author: Alejandro Ortuno, oscd.community, Huntrule Team
date: 2020-10-21
modified: 2023-09-26
tags:
  - attack.discovery
  - attack.t1046
logsource:
  product: linux
  service: auditd
  definition: Configure these rules https://github.com/Neo23x0/auditd/blob/e181243a7c708e9d579557d6f80e0ed3d3483b89/audit.rules#L182-L183
detection:
  selection:
    type: SYSCALL
    exe|endswith:
      - /telnet
      - /nmap
      - /netcat
      - /nc
      - /ncat
      - /nc.openbsd
    key: network_connect_4
  condition: selection
falsepositives:
  - Legitimate administration activities
level: low
license: DRL-1.1

Convert

This rule as a query you can run. Uses no unlock credit.

SplunkSPL