Network Connection Initiated To Cloudflared Tunnels Domains

Hunt Hypothesis

Detects network connections to Cloudflared tunnels domains initiated by a process on the system. Attackers can abuse that feature to establish a reverse shell or persistence on a machine.

Detection Rule

Sigma (Original)

title: Network Connection Initiated To Cloudflared Tunnels Domains
id: 7cd1dcdc-6edf-4896-86dc-d1f19ad64903
related:
    - id: a1d9eec5-33b2-4177-8d24-27fe754d0812
      type: derived
status: test
description: |
    Detects network connections to Cloudflared tunnels domains initiated by a process on the system.
    Attackers can abuse that feature to establish a reverse shell or persistence on a machine.
references:
    - https://defr0ggy.github.io/research/Abusing-Cloudflared-A-Proxy-Service-To-Host-Share-Applications/
    - https://www.guidepointsecurity.com/blog/tunnel-vision-cloudflared-abused-in-the-wild/
    - Internal Research
author: Kamran Saifullah, Nasreddine Bencherchali (Nextron Systems)
date: 2024-05-27
tags:
    - attack.exfiltration
    - attack.command-and-control
    - attack.t1567
    - attack.t1572
logsource:
    category: network_connection
    product: windows
detection:
    selection:
        Initiated: 'true'
        DestinationHostname|endswith:
            - '.v2.argotunnel.com'
            - 'protocol-v2.argotunnel.com'
            - 'trycloudflare.com'
            - 'update.argotunnel.com'
    condition: selection
falsepositives:
    - Legitimate use of cloudflare tunnels will also trigger this.
level: medium

KQL (Azure Sentinel)

imNetworkSession
| where NetworkDirection =~ "true" and (DstHostname endswith ".v2.argotunnel.com" or DstHostname endswith "protocol-v2.argotunnel.com" or DstHostname endswith "trycloudflare.com" or DstHostname endswith "update.argotunnel.com")

Required Data Sources

False Positive Guidance

• Legitimate use of cloudflare tunnels will also trigger this.

MITRE ATT&CK Context

• Tactic: Exfiltration
• Tactic: Command and Control
• Technique: T1567 — T1567
• Technique: T1572 — T1572

References

• https://defr0ggy.github.io/research/Abusing-Cloudflared-A-Proxy-Service-To-Host-Share-Applications/
• https://www.guidepointsecurity.com/blog/tunnel-vision-cloudflared-abused-in-the-wild/
• Internal Research
• SigmaHQ Rule