sshd does not start with KexAlgorithms paramater

[scotsman88]

Prerequisites

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Steps to reproduce

When I add the parameter "KexAlgorithms" in the sshd_config, the service fails to start.
I want to add legacy support for key methods.

KexAlgorithms curve25519-sha256@libssh.org,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group14-sha1,diffie-hellman-group-exchange-sha1,diffie-hellman-group1-sha1

service works fine when not using that parameter

Expected behavior

sshd.exe should start

Actual behavior

Service fails to start
Error 1067: the process terminated unexpectedly

Error details

No response

Environment data

N/A

Version

OpenSSH_for_Windows_8.1p1, LibreSSL 2.9.2 (Windows Server 2016 DC)

Visuals

No response

[vthiebaut10]

@scotsman88 I was unable to repro this behavior. The KexAlgorithms that you provided in this issue should work.

However, Error 1067 often indicates that there is a formatting error in the sshd_config. I suggest you run sshd in Debug mode, so that you get a more helpful error message. (Instructions here: https://github.com/PowerShell/Win32-OpenSSH/wiki/Troubleshooting-Steps)
E.g.
PS C:\Program Files\OpenSSH> .\sshd.exe -ddd

Alternatively, feel free to share your sshd_config that is causing this error with us so that we can help you debug.

[ududsv]

I had exactly the same problem that was indeed a formatting issue. In my sshd_config file few "Match" blocks were already present at the end of the file, and after adding "KexAlgorithms +diffie-helleman-group14-sha1" as the last line the sshd service failed to start.

".\sshd.exe -ddd" provided clear error description - KexAlgorithms is not allowed within the Match block, and the solution was to move this line above all Match blocks.

[vthiebaut10]

Closing this issue as there was no response and the provided workaround worked for other users.