I ran into trouble connecting to some old network gear this week. It seems that the hmac-sha1 MAC was removed from the default client connection settings. And then next I was having some trouble with the host key algorithm--the host key algorithm ssh-rsa was removed too. They are still supported so can be specified manually in the client config file, such as this set that I use for older Extreme switches:
Host switch-1.domain.tld KexAlgorithms diffie-hellman-group1-sha1 HostKeyAlgorithms ssh-dss Ciphers aes256-cbc MACs hmac-sha1 HostKeyAlgorithms ssh-rsa
The errors I was getting:
Unable to negotiate with 192.168.1.1 port 22: no matching MAC found. Their offer: hmac-sha1,hmac-md5,hmac-sha1-96,hmac-md5-96
Unable to negotiate with 192.168.1.1 port 22: no matching host key type found. Their offer: ssh-rsa
You can see the difference in old and new ssh -vv outputs:
A Windows Server 2022 example:
OpenSSH_for_Windows_8.1p1, LibreSSL 3.0.2<snip>debug2: KEX algorithms: curve25519-sha256,curve25519-sha256@libssh.org,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,diffie-hellman-group14-sha256,diffie-hellman-group14-sha1,ext-info-cdebug2: host key algorithms: ecdsa-sha2-nistp256-cert-v01@openssh.com,ecdsa-sha2-nistp384-cert-v01@openssh.com,ecdsa-sha2-nistp521-cert-v01@openssh.com,ssh-ed25519-cert-v01@openssh.com,rsa-sha2-512-cert-v01@openssh.com,rsa-sha2-256-cert-v01@openssh.com,ssh-rsa-cert-v01@openssh.com,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,ssh-ed25519,rsa-sha2-512,rsa-sha2-256,ssh-rsadebug2: ciphers ctos: chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.comdebug2: ciphers stoc: chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.comdebug2: MACs ctos: umac-64-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-sha1-etm@openssh.com,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-sha1debug2: MACs stoc: umac-64-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-sha1-etm@openssh.com,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-sha1
Freshly updated (2024-10-15) Windows 11 example:
OpenSSH_for_Windows_9.5p1, LibreSSL 3.8.2<snip>debug2: KEX algorithms: curve25519-sha256,curve25519-sha256@libssh.org,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,diffie-hellman-group14-sha256,ext-info-c,kex-strict-c-v00@openssh.comdebug2: host key algorithms: ssh-ed25519-cert-v01@openssh.com,ecdsa-sha2-nistp256-cert-v01@openssh.com,ecdsa-sha2-nistp384-cert-v01@openssh.com,ecdsa-sha2-nistp521-cert-v01@openssh.com,sk-ssh-ed25519-cert-v01@openssh.com,sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,rsa-sha2-512-cert-v01@openssh.com,rsa-sha2-256-cert-v01@openssh.com,ssh-ed25519,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,sk-ssh-ed25519@openssh.com,sk-ecdsa-sha2-nistp256@openssh.com,rsa-sha2-512,rsa-sha2-256debug2: ciphers ctos: chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.comdebug2: ciphers stoc: chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.comdebug2: MACs ctos: umac-64-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512debug2: MACs stoc: umac-64-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512
The changes can be found in the myproposal.h file. Below is a before and after of the MAC section since the diffs on GitHub seemed confusing to me.
Before:
#define KEX_SERVER_MAC \ "umac-64-etm@openssh.com," \ "umac-128-etm@openssh.com," \ "hmac-sha2-256-etm@openssh.com," \ "hmac-sha2-512-etm@openssh.com," \ "hmac-sha1-etm@openssh.com," \ "umac-64@openssh.com," \ "umac-128@openssh.com," \ "hmac-sha2-256," \ "hmac-sha2-512," \ "hmac-sha1"
After:
#ifdef WINDOWS#define KEX_SERVER_MAC \ "umac-64-etm@openssh.com," \ "umac-128-etm@openssh.com," \ "hmac-sha2-256-etm@openssh.com," \ "hmac-sha2-512-etm@openssh.com," \ "umac-64@openssh.com," \ "umac-128@openssh.com," \ "hmac-sha2-256," \ "hmac-sha2-512,"#else#define KEX_SERVER_MAC \ "umac-64-etm@openssh.com," \ "umac-128-etm@openssh.com," \ "hmac-sha2-256-etm@openssh.com," \ "hmac-sha2-512-etm@openssh.com," \ "hmac-sha1-etm@openssh.com," \ "umac-64@openssh.com," \ "umac-128@openssh.com," \ "hmac-sha2-256," \ "hmac-sha2-512," \ "hmac-sha1"#endif
They did an #IFDEF so that this only affects the Windows client.
And the changes for the ssh-rsa setting were made way back in 2021 yet took until now to reach my PC.