I'm trying to use ncat to connect between virtual windows7 and linux machines.

On linux:

ncat -vnl 4444 --ssl

On windows:

ncat -v 4444 --ssl

And when I try to connect from the client I get this error:

Ncat: Failed SSL connection from error:1417D102:SSL routines:
tls_process_client_hello:unsupported protocol

Things I tried that did not work:

  • Adding extra parameters --ssl-cert test-cert.pem --ssl-key test-key.pem
  • Trying the other way around(linux client, windows server) I also googled a lot but, but I couldnt find a real solution, its all what might be wrong.

I can make this work using openssl s_client. But I need to use ncat, how can I solve this problem?

migrated from security.stackexchange.com Dec 13 '17 at 10:37

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  • what version is the ncat on windows? try getting an ncat of the same version as the linux one. – ztk Dec 8 '17 at 18:28

The problem is that the Linux ncat server will only use TLS1.2 for SSL connections. The Windows ncat is not using TLS1.2. This causes the unsupported protocol error.

I can replicate this issue using ncat version 7.60 on linux and connecting to it with openssl s_client using different protocol options. ncat 7.60 only uses tls1.2 for ssl connections.

To make this work using ncat, install the same version of ncat on both systems.

  • s_client is one option, changing ncat versions so that they match is another. – ztk Dec 8 '17 at 18:40
  • changing versions is not possible – Spring Dec 8 '17 at 18:49
  • @Spring Well, this answer explains that the versions are incompatible. If changing versions is not an option, you're out of luck. Is there a particular reason why you can't change the setup? – Arminius Dec 8 '17 at 19:48
  • @Arminius that's pentest virtual lab environment, not recommended to update/downgrade any software – Spring Dec 8 '17 at 21:28

As it seems that you are coming from PWK, check out Errata on their forum.

From their forum it seems that openssl s_client is acceptable, at least until this issue gets resolved on windows7 virtual machine.

In case you really need to use ncat, upgrade to up-to date version should help.

  • "I can make this work using openssl s_client. But I need to use ncat, how can I solve this problem?" Can you clarify how your answer addresses the question? It would help to flesh out the "how", and add a link for your reference. – fixer1234 Jun 26 '18 at 20:34

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