Zeek: Public RDP Connections from Non-Private IPv4/IPv6 Ranges

Alert on Zeek-observed RDP connections originating from non-excluded IP ranges, suggesting external accessibility.

FreeReviewedSigma · High · v2

Product: zeek
Service: rdp
Author: Josh Brower @DefensiveDepth (SigmaHQ), DRL 1.1
Published: 2020-08-22
Updated: 2026-07-31

ATT&CK techniques

Lateral Movement

Recon
Resource Dev
Initial Access
Execution
Persistence
Priv Esc
Defense Evasion
Cred Access
Discovery
Lateral Movement
- T1021.001Remote Desktop Protocol
Collection
C2
Exfiltration
Impact

What it detects

This rule flags RDP connection attempts where the source IP is in routable or non-routable categories excluded from private or loopback ranges, indicating possible externally reachable RDP access. Attackers may probe or attempt lateral movement via exposed remote desktop services, making unintended exposure a key risk. It relies on Zeek RDP service connection telemetry, using the origin IP address to determine whether the connection matches the specified CIDR ranges.

Reporting behind it

github.comhttps://github.com/SigmaHQ/sigma/blob/master/rules/network/zeek/zeek_rdp_public_listener.yml

Related detections9 linkedT1021.001 — drag to rearrange

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Suspicious Firewall Rule Allowing SSH via New-NetFirewallRule During Ransomware

Malicious RDP Tunneling via ngrok (via process_creation)

Suspicious Remote Desktop Enablement via Registry By Ransomware

Suspicious Remote Desktop Enablement via netsh Firewall Rule (via process_creation)

Suspicious RDP Enablement via netsh Firewall Rule

Suspicious RDP Enablement via fDenyTSConnections Registry Modification

Suspicious RDP Enablement via fDenyTSConnections Registry Modification [Huntress] #2

Zeek: Public RDP Connections from Non-Private IPv4/IPv6 Ranges

Pivot detection · T1021.001 · 9 related

Changelog

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.

zeek-rdp-connections-from-non-routable-public-ip-ranges-1fc0809e

title: "Zeek: Public RDP Connections from Non-Private IPv4/IPv6 Ranges"
id: 645e021e-1ecb-4b15-ae47-8b845192d8d8
status: test
description: This rule flags RDP connection attempts where the source IP is in routable or non-routable categories excluded from private or loopback ranges, indicating possible externally reachable RDP access. Attackers may probe or attempt lateral movement via exposed remote desktop services, making unintended exposure a key risk. It relies on Zeek RDP service connection telemetry, using the origin IP address to determine whether the connection matches the specified CIDR ranges.
author: Josh Brower @DefensiveDepth, Huntrule Team
date: 2020-08-22
modified: 2024-03-13
tags:
  - attack.lateral-movement
  - attack.t1021.001
logsource:
  product: zeek
  service: rdp
detection:
  selection:
    id.orig_h|cidr:
      - ::1/128
      - 10.0.0.0/8
      - 127.0.0.0/8
      - 172.16.0.0/12
      - 192.168.0.0/16
      - 169.254.0.0/16
      - 2620:83:8000::/48
      - fc00::/7
      - fe80::/10
  condition: not selection
falsepositives:
  - Although it is recommended to NOT have RDP exposed to the internet, verify that this is a) allowed b) the server has not already been compromised via some brute force or remote exploit since it has been exposed to the internet. Work to secure the server if you are unable to remove it from being exposed to the internet.
level: high
license: DRL-1.1
related:
  - id: 1fc0809e-06bf-4de3-ad52-25e5263b7623
    type: derived
references:
  - https://github.com/SigmaHQ/sigma/blob/master/rules/network/zeek/zeek_rdp_public_listener.yml

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