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ATT&CK Technique

Port Knocking

T1205.001 · stealth, persistence, command-and-control

Adversaries may use port knocking to hide open ports used for persistence or command and control. To enable a port, an adversary sends a series of attempted connections to a predefined sequence of closed ports. After the sequence is completed, opening a port is often accomplished by the host based firewall, but could also be implemented by custom software.

This technique has been observed both for the dynamic opening of a listening port as well as the initiating of a connection to a listening server on a different system. The observation of the signal packets to trigger the communication can be conducted through different methods. One means, originally implemented by Cd00r, is to use the libpcap libraries to sniff for the packets in question.

Another method leverages raw sockets, which enables the malware to use ports that are already open for use by other programs.

LinuxmacOSNetwork DevicesWindows
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Actors Using This

2
china_state_sponsored_mandiant_unc3886_virtualization_firewall_zero_day_specialistUNC3886
china_state_sponsored_mandiant_unc4841_barracuda_esg_zero_day_specialistUNC4841
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Mitigations

1
MITRE ATT&CK mitigations - vendor-agnostic guidance for reducing exposure to this technique.
M1037Filter Network Traffic

Employ network appliances and endpoint software to filter ingress, egress, and lateral network traffic. This includes protocol-based filtering, enforcing firewall rules, and blocking or restricting traffic based on predefined conditions to limit adversary movement and data exfiltration.

Ingress Traffic Filtering
  • Use Case: Configure network firewalls to allow traffic only from authorized IP addresses to public-facing servers.
  • Implementation: Limit SSH (port 22) and RDP (port 3389) traffic to specific IP ranges.
Egress Traffic Filtering
  • Use Case: Use firewalls or endpoint security software to block unauthorized outbound traffic to prevent data exfiltration and command-and-control (C2) communications.
  • Implementation: Block outbound traffic to known malicious IPs or regions where communication is unexpected.
Protocol-Based Filtering
  • Use Case: Restrict the use of specific protocols that are commonly abused by adversaries, such as SMB, RPC, or Telnet, based on business needs.
  • Implementation: Disable SMBv1 on endpoints to prevent exploits like EternalBlue.
Network Segmentation
  • Use Case: Create network segments for critical systems and restrict communication between segments unless explicitly authorized.
  • Implementation: Implement VLANs to isolate IoT devices or guest networks from core business systems.
Application Layer Filtering
  • Use Case: Use proxy servers or Web Application Firewalls (WAFs) to inspect and block malicious HTTP/S traffic.
  • Implementation: Configure a WAF to block SQL injection attempts or other web application exploitation techniques.
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Detection Coverage

1/6 layers
Coverage across standard detection surfaces. Rows marked none have no rule of that type mapped. Some are real blind spots worth closing; others are simply not applicable to this technique (e.g. YARA matches malware files, not network behaviour).
Behavioral / log (Sigma) none
Analytics (MITRE CAR) none
Runtime / container (Falco) 1
File / malware (YARA) none
Network (Suricata/Snort) none
Vuln scan (Nuclei) none
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Falco Runtime Rules

1
Container / Linux runtime detections that fire on this technique.
NOTICEUnexpected K8s NodePort Connection
Detect attempts to utilize K8s NodePorts from a container. K8s NodePorts are accessible on the eth0 interface of each node, and they facilitate external traffic into a Kubernetes cluster. Attackers could misuse them for unauthorized access. The rule uses default port ranges, but check for custom ranges and make necessary adjustments. Also, consider tuning this rule as needed.
view condition
inbound_outbound and container and fd.sport >= 30000 and fd.sport <= 32767 and not nodeport_containers
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Comply & Defend

NIST 800-53AC-03, AC-04, CA-07, CM-06, CM-07, SC-07, SI-04, SI-15
D3FEND9 defensive techniques
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External lookups - second-class, for what we don’t hold ourselves
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