I can successfully use Putty 0.70 to connect with SSH from Win10-x64 to Solaris10-x64 host, using default putty settings. But using Putty 0.71 for same machine & same (default) settings it immediately displays error "Remote side unexpectedly closed network connection". Using latest Putty 0.75 the connection attempt stalls, never finishes, no output and no errors. Any ideas or suggestions to troubleshoot?
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2Probably weak crypto, or rather, Solaris' lack of modern strong crypto.– Michael HamptonJun 4, 2021 at 17:50
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@MichaelHampton Well, to be fair Solaris 10 was introduced in January 2005. The latest version of Red Hat available at that time was 3. The Solaris installation in the question would likely support current cryptography if it were kept up-to-date...– Andrew HenleJun 6, 2021 at 1:08
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I don't admin the Solaris 10 box. Can I get Putty to produce some output that I can use to help the Solaris admin with missing updates? I tried setting the logging options, but Putty does not produce a log file. Putty just says "unexpectedly closed network connection" without creating a log file.– netjeffJun 9, 2021 at 16:25
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1 Answer
I solved my problem by unchecking the setting for "GSSAPI key exchange" to work with the Solaris10 hosts I connect to. Answering my own question for future Internet users searching with similar symptoms.
Putty 0.71 changelog includes this:
Support for GSSAPI key exchange: an alternative to the older GSSAPI authentication system [...].
The Putty 0.71 and later apparently use this by default. Disabling this setting on my connections to these Solaris10 servers solves my problems. I guess that these Solaris10 servers are so old that they totally choke when Putty tries this type of key exchange.
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FYI, I also had similar symptoms with MobaXterm. MobaXterm has a "GSSAPI Kerberos" checkbox that I had to uncheck to work with these older Solaris10 servers.– netjeffNov 4, 2021 at 20:19