Port 18Message Send Protocol
Message Send Protocol (MSP) is a legacy protocol designed primarily for transmitting short, text-based notifications between networked hosts. It facilitates simple communication by enabling users or systems to send alerts or brief messages without the need for complex email or file transfer protocols. While it once played a role in system messaging and network administrative alerts, its use today has largely been deprecated due to the prevalence of more secure and feature-rich alternatives..
- transport
- tcp · udp
- in transit
- cleartext
- assignment
- official
- risk
- 4/10
- lookups
- 8,764
2 transports registered
payload readable on path
registered with iana
caution
rank 576 of 993 · top 58%
Technical Details
what runs on :18Introduction
Message Send Protocol (MSP) operates over TCP and UDP port 18. It was created to provide straightforward message delivery across interconnected hosts by transferring a simple text payload. Unlike email protocols that involve headers, attachments, and complex formatting, MSP sends short plaintext messages without additional structure.
Operation
The protocol works by establishing a connection (over TCP) or sending datagrams (over UDP) to a listening service on port 18. The client transmits the message content, which is either displayed to the user or processed by a local application. Since there is minimal overhead, MSP ensures low-latency delivery, suitable for brief alerts or status updates rather than long-form communication.
Deployment Context
Historically, MSP served system administrators as a network-based notification tool, integrated into Unix environments and early distributed systems to send concise updates about system states, service events, or critical network alerts. Its simplicity meant low resource consumption but at the cost of lacking encryption, authentication, or advanced delivery guarantees.
Security Information
exposure of :18risk score
4/ 10caution
worth attention. how exposed you are depends on configuration — don't leave it reachable from the internet without a reason.
network services averages 3.9 across 604 ports — this one sits 0.1 above.
in transit
cleartext
credentials and payloads are readable by anyone on path
assignment
official
registered with iana for this service — scanners fingerprint it by number
reachable over
tcp · udp
udp is connectionless — source addresses are trivially spoofed and it is a reflection favourite
security overview
Common Vulnerabilities
- Lack of encryption exposes message contents to eavesdropping.
- No authentication mechanisms, making it susceptible to spoofing and impersonation.
- Possible abuse for spam or message flooding (denial-of-service attacks).
- Could be leveraged in reconnaissance by adversaries to identify active hosts running MSP.
Common Mitigations
- Disable MSP services if not explicitly required.
- Use access control lists (ACLs) or firewalls to restrict port 18 exposure.
- Replace MSP with modern, secure messaging protocols featuring encryption/authentication.
- Monitor network traffic for unusual message activity directed to port 18.
- Implement intrusion prevention systems (IPS) to block malicious MSP traffic.
Related Ports
the 8 most looked-up other ports in network services — 604 ports carry that label.
| port | service | risk | |||
|---|---|---|---|---|---|
| :9080 | Groove RPC | TCPUDP | Web Services | caution | 70.8k |
| :6543 | Jetnet | UDP | Network Services | caution | 65.3k |
| :5938 | TeamViewer | TCPUDP | Remote Access | caution | 65.0k |
| :8291 | Winbox MikroTik Admin | TCP | Security | caution | 62.9k |
| :3233 | WhiskerControl Protocol | TCPUDP | Network Services | caution | 61.9k |
| :3268 | Microsoft Global Catalog (GC) | TCPUDP | Security | caution | 54.6k |
| :135 | Microsoft EPMAP | TCPUDP | Security | caution | 51.9k |
| :3128 | Tatsoft Default HTTP Proxy | TCP | Web Services | caution | 46.8k |
risk mix of the 8 listed
- caution100%
0 of 8 encrypted