ssh kept closing after connection

[eldzee]

Hello, I'm trying to add a target host which is pretty old which uses openSSH6.0
when connecting thru warpgate, it kept failing.

the log says something about utf8error:

...
12:32:53 DEBUG writing, seqn = 17
12:32:53 DEBUG padding length 19
12:32:53 DEBUG packet_length 92
12:32:53 DEBUG SSH: read 21     session=a611a509-5a43-4674-9481-f4f04e383c88
12:32:53 DEBUG SSH: Ok("SSH-1.99-OpenSSH_6.0\n")     session=a611a509-5a43-4674-9481-f4f04e383c88
12:32:53 DEBUG SSH: bytes_read: 0     session=a611a509-5a43-4674-9481-f4f04e383c88
12:32:53 DEBUG SSH: read_ssh_id: reading     session=a611a509-5a43-4674-9481-f4f04e383c88
12:32:53 DEBUG writing, seqn = 18
12:32:53 DEBUG padding length 19
12:32:53 DEBUG packet_length 92
12:32:53 DEBUG SSH: read 256     session=a611a509-5a43-4674-9481-f4f04e383c88
12:32:53 DEBUG SSH: Err(Utf8Error { valid_up_to: 3, error_len: Some(1) })     session=a611a509-5a43-4674-9481-f4f04e383c88
12:32:53 DEBUG SSH: bytes_read: 0     session=a611a509-5a43-4674-9481-f4f04e383c88
12:32:53 DEBUG SSH: read_ssh_id: reading     session=a611a509-5a43-4674-9481-f4f04e383c88
12:32:53 DEBUG SSH: read 0     session=a611a509-5a43-4674-9481-f4f04e383c88
12:32:53 DEBUG SSH: Err(Utf8Error { valid_up_to: 3, error_len: Some(1) })     session=a611a509-5a43-4674-9481-f4f04e383c88
12:32:53 DEBUG SSH: Dropped session=a611a509-5a43-4674-9481-f4f04e383c88 session=a611a509-5a43-4674-9481-f4f04e383c88
12:32:53 ERROR SSH: Connection error error=Ssh(Disconnect) session=a611a509-5a43-4674-9481-f4f04e383c88
12:32:53 DEBUG SSH: Connect error: Disconnected session=a611a509-5a43-4674-9481-f4f04e383c88
12:32:53  INFO SSH: Client session closed session=a611a509-5a43-4674-9481-f4f04e383c88
12:32:53  INFO SSH: Closed connection session=a611a509-5a43-4674-9481-f4f04e383c88
12:32:53 DEBUG SSH: Dropped session=a611a509-5a43-4674-9481-f4f04e383c88
12:32:53 DEBUG Event event=ConnectionError(Ssh(Disconnect))
12:32:53 DEBUG Event event=Close(f4ce5191-5cde-459a-90b8-95131002f6af)
12:32:53 DEBUG Event event=State(Disconnected)
12:32:53  INFO Closed session
12:32:53 DEBUG Dropped
12:32:53 DEBUG writing, seqn = 19
12:32:53 DEBUG padding length 6
...

if I connect directly using openssh:

OpenSSH_8.9p1 Ubuntu-3ubuntu0.7, OpenSSL 3.0.2 15 Mar 2022
debug1: Reading configuration data /root/.ssh/config
debug1: /root/.ssh/config line 1: Applying options for *
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: include /etc/ssh/ssh_config.d/*.conf matched no files
debug1: /etc/ssh/ssh_config line 21: Applying options for *
debug1: Connecting to ip.add.re.ss [ip.add.re.ss] port 22.
debug1: Connection established.
debug1: identity file /root/.ssh/id_rsa type 0
debug1: identity file /root/.ssh/id_rsa-cert type -1
debug1: identity file /root/.ssh/id_ecdsa type 2
debug1: identity file /root/.ssh/id_ecdsa-cert type -1
debug1: identity file /root/.ssh/id_ecdsa_sk type -1
debug1: identity file /root/.ssh/id_ecdsa_sk-cert type -1
debug1: identity file /root/.ssh/id_ed25519 type -1
debug1: identity file /root/.ssh/id_ed25519-cert type -1
debug1: identity file /root/.ssh/id_ed25519_sk type -1
debug1: identity file /root/.ssh/id_ed25519_sk-cert type -1
debug1: identity file /root/.ssh/id_xmss type -1
debug1: identity file /root/.ssh/id_xmss-cert type -1
debug1: identity file /root/.ssh/id_dsa type -1
debug1: identity file /root/.ssh/id_dsa-cert type -1
debug1: Local version string SSH-2.0-OpenSSH_8.9p1 Ubuntu-3ubuntu0.7
debug1: Remote protocol version 1.99, remote software version OpenSSH_6.0
debug1: compat_banner: match: OpenSSH_6.0 pat OpenSSH* compat 0x04000000
debug1: Authenticating to ip.add.re.ss:22 as '<user>'
debug1: load_hostkeys: fopen /root/.ssh/known_hosts2: No such file or directory
debug1: load_hostkeys: fopen /etc/ssh/ssh_known_hosts: No such file or directory
debug1: load_hostkeys: fopen /etc/ssh/ssh_known_hosts2: No such file or directory
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: algorithm: ecdh-sha2-nistp256
debug1: kex: host key algorithm: ecdsa-sha2-nistp256
debug1: kex: server->client cipher: aes128-ctr MAC: [email protected] compression: none
debug1: kex: client->server cipher: aes128-ctr MAC: [email protected] compression: none
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug1: SSH2_MSG_KEX_ECDH_REPLY received
debug1: Server host key: ecdsa-sha2-nistp256 SHA256:
debug1: load_hostkeys: fopen /root/.ssh/known_hosts2: No such file or directory
debug1: load_hostkeys: fopen /etc/ssh/ssh_known_hosts: No such file or directory
debug1: load_hostkeys: fopen /etc/ssh/ssh_known_hosts2: No such file or directory
debug1: Host 'ip.add.re.ss' is known and matches the ECDSA host key.
debug1: Found key in /root/.ssh/known_hosts:xx
debug1: rekey out after 4294967296 blocks
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: rekey in after 4294967296 blocks
debug1: Will attempt key: /root/.ssh/id_rsa RSA SHA256:
debug1: Will attempt key: /root/.ssh/id_ecdsa ECDSA SHA256:
debug1: Will attempt key: /root/.ssh/id_ecdsa_sk
debug1: Will attempt key: /root/.ssh/id_ed25519
debug1: Will attempt key: /root/.ssh/id_ed25519_sk
debug1: Will attempt key: /root/.ssh/id_xmss
debug1: Will attempt key: /root/.ssh/id_dsa
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: publickey,password,keyboard-interactive
debug1: Next authentication method: publickey
debug1: Offering public key: /root/.ssh/id_rsa RSA SHA256:
debug1: Authentications that can continue: publickey,password,keyboard-interactive
debug1: Offering public key: /root/.ssh/id_ecdsa ECDSA SHA256:
debug1: Authentications that can continue: publickey,password,keyboard-interactive
debug1: Trying private key: /root/.ssh/id_ecdsa_sk
debug1: Trying private key: /root/.ssh/id_ed25519
debug1: Trying private key: /root/.ssh/id_ed25519_sk
debug1: Trying private key: /root/.ssh/id_xmss
debug1: Trying private key: /root/.ssh/id_dsa
debug1: Next authentication method: keyboard-interactive
debug1: Authentications that can continue: publickey,password,keyboard-interactive
debug1: Next authentication method: password