ssh "firma incorrecta" al conectarse al servidor

Pregunta:

Tengo un servidor al que normalmente me conecto desde varias computadoras portátiles, algunas FC22, FC23 o ubuntu. Instalé una nueva computadora portátil FC23, agregué las claves relevantes en Authorized_keys, etc:

[mathieu@xps13 code]$ ssh -vvv root@ovh6
OpenSSH_7.2p2, OpenSSL 1.0.2g-fips  1 Mar 2016
debug1: Reading configuration data /home/mathieu/.ssh/config
debug1: /home/mathieu/.ssh/config line 5: Applying options for *
debug1: /home/mathieu/.ssh/config line 71: Applying options for ovh6
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 58: Applying options for *
debug2: resolving "XXXXXXXXXXXXXXX" port 22
debug2: ssh_connect_direct: needpriv 0
debug1: Connecting to XXXXXXXXXXXXXXX [YYYYYYYYYYYY] port 22.
debug1: Connection established.
debug1: identity file /home/mathieu/.ssh/id_rsa type 1
debug1: key_load_public: No such file or directory
debug1: identity file /home/mathieu/.ssh/id_rsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/mathieu/.ssh/id_dsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/mathieu/.ssh/id_dsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/mathieu/.ssh/id_ecdsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/mathieu/.ssh/id_ecdsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/mathieu/.ssh/id_ed25519 type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/mathieu/.ssh/id_ed25519-cert type -1
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_7.2
debug1: Remote protocol version 2.0, remote software version OpenSSH_6.9
debug1: match: OpenSSH_6.9 pat OpenSSH* compat 0x04000000
debug2: fd 3 setting O_NONBLOCK
debug1: Authenticating to ns427784.ip-37-187-149.eu:22 as 'root'
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug2: local client KEXINIT proposal
debug2: KEX algorithms: curve25519-sha256@libssh.org,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,ext-info-c
debug2: host key algorithms: ssh-rsa-cert-v01@openssh.com,rsa-sha2-512,rsa-sha2-256,ssh-rsa,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,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,ssh-ed25519
debug2: ciphers ctos: chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com,aes128-cbc,aes192-cbc,aes256-cbc,3des-cbc
debug2: ciphers stoc: chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com,aes128-cbc,aes192-cbc,aes256-cbc,3des-cbc
debug2: 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-sha1
debug2: 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
debug2: compression ctos: none,zlib@openssh.com,zlib
debug2: compression stoc: none,zlib@openssh.com,zlib
debug2: languages ctos: 
debug2: languages stoc: 
debug2: first_kex_follows 0 
debug2: reserved 0 
debug2: peer server KEXINIT proposal
debug2: KEX algorithms: diffie-hellman-group-exchange-sha256,diffie-hellman-group14-sha1,diffie-hellman-group-exchange-sha1
debug2: host key algorithms: ssh-rsa
debug2: ciphers ctos: aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr,aes128-ctr
debug2: ciphers stoc: aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr,aes128-ctr
debug2: MACs ctos: hmac-sha2-512-etm@openssh.com,hmac-sha2-256-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-512,hmac-sha2-256,hmac-ripemd160
debug2: MACs stoc: hmac-sha2-512-etm@openssh.com,hmac-sha2-256-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-512,hmac-sha2-256,hmac-ripemd160
debug2: compression ctos: none,zlib@openssh.com
debug2: compression stoc: none,zlib@openssh.com
debug2: languages ctos: 
debug2: languages stoc: 
debug2: first_kex_follows 0 
debug2: reserved 0 
debug1: kex: algorithm: diffie-hellman-group-exchange-sha256
debug1: kex: host key algorithm: ssh-rsa
debug1: kex: server->client cipher: aes128-ctr MAC: umac-128-etm@openssh.com compression: none
debug1: kex: client->server cipher: aes128-ctr MAC: umac-128-etm@openssh.com compression: none
debug1: kex: diffie-hellman-group-exchange-sha256 need=16 dh_need=16
debug1: kex: diffie-hellman-group-exchange-sha256 need=16 dh_need=16
debug1: SSH2_MSG_KEX_DH_GEX_REQUEST(2048<3072<8192) sent
debug1: got SSH2_MSG_KEX_DH_GEX_GROUP
debug2: bits set: 1541/3072
debug1: SSH2_MSG_KEX_DH_GEX_INIT sent
debug1: got SSH2_MSG_KEX_DH_GEX_REPLY
debug1: Server host key: ssh-rsa SHA256:3dFTH1Rbkf+Y4PyYWfyPFkmZoxepgsdJnKgSikaSqEs
debug3: hostkeys_foreach: reading file "/home/mathieu/.ssh/known_hosts"
debug3: record_hostkey: found key type RSA in file /home/mathieu/.ssh/known_hosts:4
debug3: load_hostkeys: loaded 1 keys from XXXXXXX
debug3: hostkeys_foreach: reading file "/home/mathieu/.ssh/known_hosts"
debug3: record_hostkey: found key type RSA in file /home/mathieu/.ssh/known_hosts:4
debug3: load_hostkeys: loaded 1 keys from 37.187.149.109
debug1: Host 'XXXXXXXXXXXX' is known and matches the RSA host key.
debug1: Found key in /home/mathieu/.ssh/known_hosts:4
debug2: bits set: 1569/3072
ssh_dispatch_run_fatal: Connection to XXXXXXXXXXXXXXX port 22: incorrect signature

Más información: Puedo usar el reenvío de agentes para conectarme a este servidor rebotando en otro servidor, lo que confirma que las claves de autenticación priv / pub del lado del cliente están bien. También veo que la única diferencia entre esta computadora portátil y una que falla es la versión openssh (7.1p2 = funciona, 7.2p2 = falla). es decir, después de ejecutar la actualización dnf en la computadora portátil que funciona, comienza a fallar … Reportando como un error en fedora bugzilla. para FC23.

Ahora, esto se me escapa: todavía puedo conectarme desde otra computadora portátil FC23, ¿qué podría haber hecho mal?

Respuesta:

Según el error reportado # 1332082 , fue un error en openssh enviado en Fedora 22.

En resumen, el servidor ( openssh-6.9p1 en Fedora 22) estaba haciendo una firma sobre datos diferentes a los que esperaba el cliente ( openssh-7.2 en Fedora 23), cuando usaba el diffie-hellman-group-exchange-sha256 . La solución ya está en Bodhi y en camino a las actualizaciones de Fedora 22.

Gracias por el informe.

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