Port 13 - DAYTIME (Daytime Protocol)

Why It’s Open

Port 13 provides the Daytime Protocol service, which returns the current date and time in human-readable format. It’s used for time synchronization and system diagnostics.

Common Risks

Information disclosure
Reveals system time and timezone information
Amplification attacks
Can be used in reflection DDoS attacks
Network reconnaissance
Helps map network infrastructure
System fingerprinting
Time format may reveal OS details
Resource consumption
Excessive requests can impact performance

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Enumeration & Testing

Service Detection:

nmap -sV -p 13

Time Query:

nc  13

UDP Time Query:

nc -u  13

What to Look For

Checkpoint	What it means
Time format	Date/time string format and timezone
Service availability	TCP/UDP protocol support
Rate limiting	Response to rapid consecutive requests
Error handling	Behavior with malformed requests

Mitigation

Disable daytime service
Remove unnecessary time services
Use NTP instead
Implement proper Network Time Protocol
Firewall restrictions
Block external access to port 13
Monitor usage
Log and analyze daytime service requests
Rate limiting
Implement request throttling

TL;DR

Port 13 = Daytime Protocol service
Protocol: TCP/UDP
Used for: Returns human-readable date and time
Security focus: Proper configuration and monitoring required

Known CVEs and Exploits

DDoS amplification attacks – Daytime service used for traffic amplification and reflection attacks
Information disclosure vulnerabilities – System time and timezone information exposure for reconnaissance
Service abuse for network scanning – Used by attackers to map network infrastructure and identify active hosts
Resource exhaustion attacks – Excessive daytime requests causing denial of service conditions