TCP Port 4444 – Metasploit Default Listener (informal / malware-associated)
Port 4444 has no canonical legitimate service in modern networks. Its IANA registrations are obscure historical artifacts (krb524, the Kerberos version 4-to-5 ticket conversion service, and nv-video, an early-1990s networked video tool), and neither is encountered in current deployments. The port’s everyday significance is something else entirely: it is the default listener port used by the Metasploit Framework, the most widely-deployed open-source penetration testing toolkit.
Metasploit was created by HD Moore in 2003 and has since become the standard tool for both penetration testers and security researchers. The framework’s default reverse-shell handler module listens on TCP/4444 unless the operator explicitly changes it, and that default has propagated through more than two decades of training material, exploit modules, and tutorials. As a result, “a shell on 4444” became an informal shorthand in security circles for a successful exploit landing.
The port’s association extends beyond Metasploit itself. Penetration testing exercises, capture-the-flag competitions, and security training labs frequently use port 4444 for the same reverse-shell pattern. Malware authors have also used the port, sometimes deliberately to imitate pen-test traffic and confuse defenders, sometimes simply because they copy Metasploit-style boilerplate without changing the defaults.
Outbound TCP/4444 from end-user devices is uncommon and usually worth investigating. Inbound TCP/4444 to a host that does not have a specific reason to listen on this port is unusual and is widely treated as either an intentional pen-test setup, a forgotten testing artifact, or a sign of unauthorized software running on the host.
UDP/4444 is also defined in the IANA registry under the same legacy assignments but is not used in practice.
About TCP Port 4444
The Internet Assigned Numbers Authority (IANA) registers port 4444 for krb524. The IANA description reads: ‘KRB524’.
Security Considerations
Port 4444 is one of the most-watched ports in defensive security tooling, despite having only one IDS rule in our specific dataset. The reason for the watchfulness is the Metasploit association described in the plain summary: any unexpected service listening on TCP/4444 is treated as suspicious by default, and any unexpected outbound connection to TCP/4444 from a managed workstation is a common alerting condition for security teams.
Our data shows 1 IDS rule referencing this port, detecting backdoor activity from the Reptile Linux LKM rootkit. Reptile is a loadable kernel module that hides files, processes, and network connections from system tools while providing a remote backdoor. The malware is mapped to MITRE ATT&CK Software S1219.
Reptile’s use of port 4444 follows the broader pattern. Malware that needs a listener port often picks 4444 because of the Metasploit association: the port already attracts attention, and the attention paid to it by defenders is often calibrated to Metasploit-specific patterns rather than to the actual malware behavior on the host. Conversely, sophisticated malware may deliberately avoid the port for the same reason. The result is a population skew where 4444-listener malware tends to be either lower-tier opportunistic tooling or specifically crafted to imitate pen-test traffic for confusion value.
This dual-use creates a long-running operational issue for blue teams: a pen test in progress and a real compromise can produce identical-looking observations on the wire. The mitigation is process, not technology. Authorized testing should be tracked in a ticketing system with start and end times, source addresses, and target scope. Detection of port-4444 traffic outside that authorized window should trigger investigation rather than dismissal.
Defensive practice for ordinary networks is straightforward. No production service should listen on TCP/4444 outside of authorized testing environments. Outbound TCP/4444 from end-user workstations to internet destinations is high-priority. Incident-response procedures should treat unexpected 4444 activity as a real finding by default and use ticketing data to confirm or rule out an authorized test, rather than the other way around.
IDS Rule References
1 IDS / security rule reference TCP port 4444. Presence in IDS rules does not mean traffic on this port is malicious. These are patterns security tools monitor.
Rule categories (top 1): trojan-activity (1).
Sample rule descriptions for TCP port 4444:
- ET MALWARE Reptile Linux LKM Rootkit Backdoor Activity
Malware Activity
Some malware indicators are observed on this port.
1 of 1 IDS rule for TCP port 4444 involve malware activity.
Families observed (top 1): Reptile (1).
Data Sources
This information is compiled from: IANA Service Name and Transport Protocol Port Number Registry, Emerging Threats Open Ruleset (BSD 2-Clause / GPLv2 per SID range), and MITRE ATT&CK (Apache 2.0).