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AKA RegreSSHion. Affected versions of OpenSSH are vulnerable to a unauthenticated, remote code execution vulnerability, that allows an attacker to get root access on the machine.
You're affected if you are using a vulnerable version of OpenSSH and you expose your SSH server on the internet on port 22.
Disallow all traffic on port 22 except your own IP. Upgrade OpenSSH to a patched version when they are available.