The Port That Does Not Exist
Port 0, a port that does not exist, is often used by malware and other malicious actors to hide their activities. Despite being reserved, it can still be used as a destination port in TCP headers, and tools such as scanners and web browsers will refuse or block packets addressed to it. A study conducted on the entire internet found that only a small percentage of IP addresses responded to SYN packets sent to port 0, suggesting that it is not commonly used for legitimate purposes.
The study also discovered that many of the responding IPs were part of network devices such as firewalls and routers. While some programs can bypass the restrictions on port 0, it is generally considered a bad idea and is not recommended for use.
Written by urgent.news from Lobsters's reporting — not their text. Machine-written — may contain errors; check the original before relying on it.
