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MITRE ATT&CK® Technique

T1205.001: Port Knocking

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 [1], 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.

EnterpriseT1205.001Sub-techniqueObject v2.0Modified
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Glexia's Take · Automated analysis

Security context for executives and security teams

Automation confidenceMedium

T1205.001: Port Knocking describes 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 ...

Executive priority

T1205.001: Port Knocking is an official MITRE ATT&CK technique. Glexia treats it as defensive behavior context for prioritizing monitoring, control validation, and response planning without using the object by itself as an attribution claim.

Technical view

Security teams should validate T1205.001: Port Knocking by reviewing the official ATT&CK relationships, mapped tactics (stealth, persistence, command-and-control), supported platforms (Linux, macOS, Network Devices, Windows), and available local telemetry before making detection or mitigation decisions.

Likely telemetry

  • Official ATT&CK relationships and object metadata
  • Identity, privilege, and authentication events
  • Network, endpoint, and security-tool telemetry

Detection direction

  • Validate whether T1205.001: Port Knocking appears in your detection coverage and tabletop scenarios.
  • Use the object to align executive risk language with SOC, incident response, and detection engineering work.
  • Do not treat ATT&CK relationship context as attribution without corroborating evidence.

Mitigation priorities

  • Map the object to existing controls and identify missing telemetry or response ownership.
  • Prioritize mitigations that reduce exposure on the listed platforms and tactics.
  • Review adjacent ATT&CK relationships before changing policy, detections, or reporting language.
Additional notes and limits

Baseline Glexia take generated from the official MITRE ATT&CK STIX object, source hash, tactics, platforms, and detection fields. It is safe to replace with a richer model-generated take for the same source hash later.

This baseline take is source-grounded and schema-validated, but it does not include environment-specific telemetry, incident evidence, or threat-intelligence corroboration.

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Official MITRE ATT&CK definition

Port Knocking

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 [1], 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.

View the same entry on attack.mitre.org (MITRE-hosted reference; in-page links above use the Glexia ATT&CK library.)

Glexia analysis

How security teams should use this page

Treat this object as behavior context, not an attribution claim. Validate the related groups, software, data sources, and mitigations against official ATT&CK relationships and your own telemetry before making control-coverage decisions.

ATT&CK relationship table

Related techniques

This mirrors the MITRE pattern of making group, software, campaign, and technique relationships scannable. Relationship notes come from mirrored ATT&CK relationship text when available.

1 rows
DomainIDNameRelationship / procedure
EnterpriseT1205Traffic SignalingThis object subtechnique of Traffic Signaling.
Associated objects

Groups, software, and campaigns

GroupEnterprise

G1048: UNC3886

UNC3886 is a China-nexus cyberespionage group that has been active since at least 2022, targeting defense, technology, and telecommunication organizations located in the United States and the Asia-Pacific-Japan (APJ) regions. UNC3886 has displayed a deep understanding of edge devices and virtualization technologies through the exploitation of zero-day vulnerabilities and the use of novel malware families and utilities.[1][2]

GroupEnterprise

G0056: PROMETHIUM

PROMETHIUM is an activity group focused on espionage that has been active since at least 2012. The group has conducted operations globally with a heavy emphasis on Turkish targets. PROMETHIUM has demonstrated similarity to another activity group called NEODYMIUM due to overlapping victim and campaign characteristics.[1][2][3]

MalwareEnterprise

S1204: cd00r

cd00r is an open-source backdoor for UNIX and UNIX-variant operating systems that was orginally released in 2000. cd00r source code is primarily based on a packet-capturing program as it utilizes a sniffer to listen for specific sequences of network traffic or "secret knock" before executing the attacker's code.[1][2]

Network Devices
MalwareEnterprise

S1060: Mafalda

Mafalda is a flexible interactive implant that has been used by Metador. Security researchers assess the Mafalda name may be inspired by an Argentinian cartoon character that has been popular as a means of political commentary since the 1960s. [1]

Windows
MalwareEnterprise

S1219: REPTILE

REPTILE is an open-source Linux rootkit with multiple components that provides backdoor access and functionality.[1]

Linux
Relationship explorer

All related ATT&CK context

mitigates · MitigationM1037: Filter Network TrafficEnterpriseuses · GroupG1048: UNC3886Enterpriseuses · GroupG0056: PROMETHIUMEnterpriseuses · MalwareS1204: cd00rEnterpriseuses · MalwareS1060: MafaldaEnterpriseuses · MalwareS1219: REPTILEEnterpriseuses · MalwareS1059: metaMainEnterprisesubtechnique of · TechniqueT1205: Traffic SignalingEnterprisedetects · Detection StrategyDET0302: Port-knock → rule/daemon change → first successful connect (T1205.001)Enterprise
Mitigations

Mitigation direction

MitigationEnterprise

M1037: Filter 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. This mitigation can be implemented through the following measures:

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.

Change history

Object version and sync metadata

The fields below describe the current mirrored snapshot. When Glexia retains multiple ATT&CK source imports, you can open the table to compare the same object across releases (hashes and MITRE timestamps). For MITRE’s own release notes and roadmap, see ATT&CK resources — Updates.

ATT&CK release
19.2
Object version
2.0
Created
Modified
Raw hash
aaa0b77b0d8c964e...
Imported snapshots across ATT&CK releases(3)
ReleaseBundle importedObject versionModifiedStatusRaw hash
20.02.0Older bundleaaa0b77b0d8c…
19.22.0Current bundleaaa0b77b0d8c…
19.12.0Older bundleaaa0b77b0d8c…
Raw source

Mirrored ATT&CK source object

The raw object is retained through the mirrored ATT&CK source bundle and object hash. The raw endpoint returns the exact object from the mirrored bundle when available.

Open mirrored raw JSONOpen MITRE-hosted copy
Source references

External references and citations

MITRE external references are preserved separately from Glexia analysis so citations remain traceable to their original source records.

  1. [1]
    Hartrell cd00r 2002

    Hartrell, Greg. (2002, August). Get a handle on cd00r: The invisible backdoor. Retrieved October 13, 2018.

    Open source URL
  2. [2]
    mitre-attackT1205.001
    Open source URL
Source and licensing

Source: MITRE ATT&CK®. © 2026 The MITRE Corporation. This work is reproduced and distributed with the permission of The MITRE Corporation. MITRE ATT&CK and ATT&CK are registered trademarks of The MITRE Corporation. Glexia is not affiliated with or endorsed by MITRE.

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