Development / Debug
What is Port 9999?
Port 9999 is commonly used as a generic development, debugging, and testing port. Java applications frequently use port 9999 for JDWP (Java Debug Wire Protocol) remote debugging. Various development tools, testing frameworks, and temporary services use this easy-to-remember port. In penetration testing, port 9999 is sometimes used for reverse shells and listeners. Some specific applications like Urchin (web analytics) have used this port. Its memorable number makes it a popular choice for ad-hoc services and development environments.
Common Uses
- Java remote debugging (JDWP)
- Development and testing servers
- Ad-hoc service deployment
- Network testing and diagnostics
Technical Details
Copy-paste commands to check port 9999 (Development / Debug) from your terminal
Test connectivity
nc -zv example.com 9999
curl -v --max-time 5 http://example.com:9999/
telnet example.com 9999
nmap -p 9999 -sV example.com
(echo > /dev/tcp/example.com/9999) 2>/dev/null && echo "open" || echo "closed"
Open port in firewall
sudo ufw allow 9999/tcp
sudo iptables -A INPUT -p tcp --dport 9999 -j ACCEPT
sudo firewall-cmd --permanent --add-port=9999/tcp && sudo firewall-cmd --reload
Security Considerations
JDWP debugging on port 9999 provides full JVM control — never expose it beyond localhost or a trusted debug network. Attackers can execute arbitrary code through JDWP. Ensure debugging ports are disabled in production. Verify any service on this port is authorized.
Popular Ports Reference
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