Important ports and their known vulnerabilities.

File Transfer Ports

Port Service Purpose Vulnerability Vulnerability Example
20-21 FTP File transfer Often allows anonymous login; outdated versions like vsftpd 2.3.4 contain known backdoors. View example

Remote Access Ports

Port Service Purpose Vulnerability Vulnerability Example
22 SSH Secure remote management and command-line access Secure by design — traffic is encrypted, unlike Telnet. The main risk comes from weak or reused passwords, which make the service a common target for brute-force attacks. View example
23 Telnet Unencrypted remote terminal access Transmits all data, including credentials, in plaintext — the same TCP stream analysis technique shown on the Wireshark tool page (there demonstrated with HTTP) applies equally to Telnet traffic. -
3389 RDP Windows remote desktop access Frequent target for ransomware and unauthorized access attempts; historically affected by critical flaws like BlueKeep (CVE-2019-0708). -
5900 VNC Remote graphical desktop access Authentication relies solely on a password, with no username required — a common target for brute-force attacks, especially when default or weak passwords are used. View example

Web Ports

Port Service Purpose Vulnerability Vulnerability Example
443 HTTPS Encrypted web traffic (TLS/SSL over HTTP) Encryption alone doesn't guarantee safety — misconfigured TLS (outdated protocols like TLS 1.0/1.1, weak cipher suites), expired or self-signed certificates, and missing HTTP-to-HTTPS redirects (leaving port 80 as a fallback) are common weaknesses. Tools like sslscan or testssl.sh are used to audit these configurations. -
80 HTTP Unencrypted standard web traffic Unencrypted by default — form submissions and login credentials are transmitted in plaintext and can be intercepted. Demonstrated on the Wireshark tool page using TCP stream analysis. View example

Mail & DNS Ports

Port Service Purpose Vulnerability Vulnerability Example
25 SMTP Mail transmission between servers The VRFY command, when left unrestricted, allows enumeration of valid usernames — a technique demonstrated on the SSH Brute-Force attack page, where it's used to identify real accounts before attempting password attacks. View example
53 DNS Translates domain names to IP addresses Misconfigured zone transfers (AXFR) can leak an organization's entire DNS record set — including internal hostnames — to any requester. DNS also lacks built-in authentication, making it vulnerable to cache poisoning (redirecting users to malicious servers) and abuse for DDoS via amplification attacks, where small spoofed queries trigger disproportionately large responses. -

Database Ports

Port Service Purpose Vulnerability Vulnerability Example
3306 MySQL Relational database service, remote client connections Weak passwords are a common entry point — this instance was compromised using Hydra to brute-force the root account's password against a wordlist, gaining full administrative access to the database. View example
5432 PostgreSQL Relational database service, remote client connections Weak or default credentials are the primary entry point — Metasploit's postgres_payload exploit uses valid (often default) credentials to abuse a database procedure and execute arbitrary code, delivering a Meterpreter session rather than a plain shell. View example

File Sharing Ports

Port Service Purpose Vulnerability Vulnerability Example
139 & 445 SMB File and printer sharing between systems (Windows/Linux interoperability) SMB has a long history as a major exploitation target — most notably EternalBlue (CVE-2017-0144), which enabled the WannaCry ransomware outbreak. Older or misconfigured Samba installations, such as vulnerable usermap_script configurations, can allow unauthenticated remote command execution. View example