Exposed services · SSH

Is it a problem that SSH answers on port 22?

It can be.

Last read from the sources at the foot of this page.

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01

What is SSH?

Secure Shell (SSH) is an encrypted way to type commands on a server from elsewhere. It listens on port 22 and is common on web servers and network equipment.

02

Why does it matter?

Erlang Erlang/OTP SSH Server Missing Authentication for Critical Function Vulnerability 2025-06-09 Erlang Erlang/OTP SSH server contains a missing authentication for critical function vulnerability. This could allow an attacker to execute arbitrary commands without valid credentials, potentially leading to unauthenticated remote code execution (RCE).

Encryption protects the session, not the door. Anyone can try passwords against an SSH server that answers from the internet.

SSH software can also have flaws. CISA added one such flaw, which needed no valid sign-in, to its catalog of exploited flaws on 9 June 2025. CISA says it could let an attacker run commands without valid credentials.

03

What do I do about it?

  1. Limit port 22 in your firewall to the addresses that need it, or reach it only through a VPN.
  2. Turn off password sign-in on the server and use keys.
  3. Turn off direct sign-in as root.
  4. Keep the SSH software and the device it runs on updated.
Sources

Where does this come from?

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