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Old 02-15-2005, 03:06 PM   #1
Erik Thorsson
Registered: Jun 2004
Location: NYC
Distribution: Fedora Core 1
Posts: 64

Rep: Reputation: 15
Get OS version by nc

Just discovered nc.

yew:~$ echo "QUIT" | nc 22
SSH-2.0-OpenSSH_3.8.1p1 Debian-8.sarge.4
Protocol mismatch.

How do I stop this display of the OS version by OpenSSH?

Security by obscurity, right?

Old 02-15-2005, 07:40 PM   #2
Registered: May 2002
Posts: 179

Rep: Reputation: Disabled
I think it's a configure option, but I could be wrong. Might have to check out some of the source files if it's not...start with Makefiles
Old 02-16-2005, 11:22 PM   #3
Registered: Feb 2002
Location: IL
Distribution: Ubuntu currently, also Fedora, RHEL, CentOS
Posts: 111

Rep: Reputation: 15
That's not a an option in the sshd_config. You'll have to rebuild from source.

I don't see it in the configure --help option from a quick scan. You might have to edit source.

Telnet to port 22 will achieve the same thing as nc.

Fedora doesn't advertise the OS name, in case you were curious.

It appears as though version.h is the file to be edited.
I just changed mine to look like this.

/* $OpenBSD: version.h,v 1.42 2004/08/16 08:17:01 markus Exp $ */


Looks like it configured and instaled

$ telnet localhost 22

Connected to localhost (
Escape character is '^]'.

guess that works.

I love Open Source!


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