30 High‑Risk Ports to Secure and How to Safely Close Them

1. High‑Risk Ports

Exposing certain ports to the Internet can create serious security threats. Below are thirty commonly dangerous ports and their potential risks:

LDAP : port 389 – should not be exposed.

SMB : port 445 – frequently exploited.

MySQL : port 3306 – vulnerable to SQL injection.

Redis : port 6379 – should not be exposed.

FTP : port 21 – often attacked.

SSH : port 22 – often attacked.

Elasticsearch : port 9200 – should not be exposed and may have vulnerabilities.

DB2/Sybase : port 5000 – should not be exposed.

Weblogic : port 7001 – frequently exploited.

RDP : port 3389 – vulnerable to brute‑force attacks.

Rundeck : port 4440 – often exploited.

MongoDB : ports 27017/27018 – default open ports, should not be exposed.

Memcached : port 11211 – frequently exploited.

CouchDB : port 5984 – should not be exposed.

Hadoop : ports 8019/8042/9000/8088 – should not be exposed.

Zookeeper : port 3888 – frequently exploited.

Docker : port 2375 – should not be exposed.

Etcd : port 2379 – should not be exposed.

Supervisor : port 9001 – frequently exploited.

Spark : port 7077 – frequently exploited.

NFS : port 2049 – frequently exploited.

Flink : port 8081 – should not be exposed and may have vulnerabilities.

PostgreSQL : port 5432 – should not be exposed.

Oracle : port 1521 – should not be exposed.

Kafka : port 9092 – frequently exploited.

Nacos JRAFT : (port not specified) – should not be exposed and often exploited.

GlassFish : port 4848 – frequently exploited.

InfluxDB : ports 8083/8086 – should not be exposed.

Symantec pcAnywhere : ports 5631/5632 – should not be exposed.

2. Security Protection Tips

Optimize firewalls: configure rules to restrict access to dangerous ports, allowing only trusted IPs.

Minimize open ports: keep only ports required for business, close unnecessary ones to reduce attack surface.

Establish port‑service management: maintain an inventory linking ports to services, prohibit unauthorized services, require security approval before opening ports, and keep audit logs.

Limit default service ports: disable unnecessary services and ports.

3. How to Safely Close These Ports

Closing unnecessary ports reduces security risk. Follow these steps:

Step 1: Identify Open Ports

Use tools such as netstat, nmap or lsof to list open ports:

netstat -tuln

Step 2: Stop Related Services

Find services bound to risky ports and stop them. Example for FTP:

sudo systemctl stop vsftpd</code>
<code>sudo systemctl disable vsftpd

Step 3: Configure the Firewall

Block access to dangerous ports with firewall tools (iptables, ufw, etc.). Example to block FTP (port 21) with ufw:

sudo ufw deny 21

Step 4: Disable Unnecessary Services

Use the system service manager to disable services you do not need. Example for Telnet:

sudo systemctl stop telnet</code>
<code>sudo systemctl disable telnet

Step 5: Regular Checks

Periodically scan your system to ensure no unnecessary ports have been reopened.

Conclusion

By identifying high‑risk ports, applying protective measures, and closing unnecessary ports, you can significantly lower the risk of attacks. Network security is an ongoing process; regular reviews and updates of defenses are essential to keep your environment safe.