Created attachment 2995 [details] wireshark trace for key exchange init packet I have a 7.5p1 server with the following MACs: MACs hmac-sha2-512-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512,hmac-sha2-256 in the sshd_config I am using a 7.5p1 client as below: ssh -m hmac-sha1 user@<IP> It lets me connect. Although as per RFC https://www.ietf.org/rfc/rfc4253.txt It should just disconnect. I have attached wireshark screen shots for client and server "Key Exchange Init" packets which list the relevant contents. OS: Centos 7 SSH version: 7.5 p1
Created attachment 2996 [details] server Key Exchange Init Packet
The PNG files you uploaded are corrupt and I can't view them. Please attach a debug trace from the client instead, i.e. "ssh -vvv -m hmac-sha1 user@ip"
Amazing response time. Thanks ! I would like to mention that we have the below macs configured on the server(which is also 7.5p1): MACs hmac-sha2-512-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512,hmac-sha2-25 I stopped at the password but I can connect. -Nitin ************************** [nitin@localhost ~]$ ssh -vvv -m hmac-sha1 nitin@15.214.245.237 OpenSSH_7.5p1, OpenSSL 1.0.1e-fips 11 Feb 2013 debug1: Reading configuration data /usr/local/etc/ssh_config debug2: resolving "15.214.245.237" port 22 debug2: ssh_connect_direct: needpriv 0 debug1: Connecting to 15.214.245.237 [15.214.245.237] port 22. debug1: Connection established. debug1: identity file /home/nitin/.ssh/id_rsa type 1 debug1: key_load_public: No such file or directory debug1: identity file /home/nitin/.ssh/id_rsa-cert type -1 debug1: key_load_public: No such file or directory debug1: identity file /home/nitin/.ssh/id_dsa type -1 debug1: key_load_public: No such file or directory debug1: identity file /home/nitin/.ssh/id_dsa-cert type -1 debug1: key_load_public: No such file or directory debug1: identity file /home/nitin/.ssh/id_ecdsa type -1 debug1: key_load_public: No such file or directory debug1: identity file /home/nitin/.ssh/id_ecdsa-cert type -1 debug1: key_load_public: No such file or directory debug1: identity file /home/nitin/.ssh/id_ed25519 type -1 debug1: key_load_public: No such file or directory debug1: identity file /home/nitin/.ssh/id_ed25519-cert type -1 debug1: Enabling compatibility mode for protocol 2.0 debug1: Local version string SSH-2.0-OpenSSH_7.5 debug1: Remote protocol version 2.0, remote software version OpenSSH_7.5 debug1: match: OpenSSH_7.5 pat OpenSSH* compat 0x04000000 debug2: fd 3 setting O_NONBLOCK debug1: Authenticating to 15.214.245.237:22 as 'nitin' debug3: hostkeys_foreach: reading file "/home/nitin/.ssh/known_hosts" debug3: record_hostkey: found key type ECDSA in file /home/nitin/.ssh/known_hosts:7 debug3: load_hostkeys: loaded 1 keys from 15.214.245.237 debug3: order_hostkeyalgs: prefer hostkeyalgs: ecdsa-sha2-nistp256-cert-v01@openssh.com,ecdsa-sha2-nistp384-cert-v01@openssh.com,ecdsa-sha2-nistp521-cert-v01@openssh.com,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521 debug3: send packet: type 20 debug1: SSH2_MSG_KEXINIT sent debug3: receive packet: type 20 debug1: SSH2_MSG_KEXINIT received debug2: local client KEXINIT proposal 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-group-exchange-sha1,diffie-hellman-group14-sha256,diffie-hellman-group14-sha1,ext-info-c debug2: host key algorithms: ecdsa-sha2-nistp256-cert-v01@openssh.com,ecdsa-sha2-nistp384-cert-v01@openssh.com,ecdsa-sha2-nistp521-cert-v01@openssh.com,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,ssh-ed25519-cert-v01@openssh.com,ssh-rsa-cert-v01@openssh.com,ssh-ed25519,rsa-sha2-512,rsa-sha2-256,ssh-rsa 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 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 debug2: MACs ctos: hmac-sha1 debug2: MACs stoc: 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: 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 debug2: host key algorithms: ssh-rsa,rsa-sha2-512,rsa-sha2-256,ecdsa-sha2-nistp256,ssh-ed25519 debug2: ciphers ctos: chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com debug2: ciphers stoc: chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com debug2: MACs ctos: hmac-sha2-512-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512,hmac-sha2-256 debug2: MACs stoc: hmac-sha2-512-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512,hmac-sha2-256 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: curve25519-sha256 debug1: kex: host key algorithm: ecdsa-sha2-nistp256 debug1: kex: server->client cipher: chacha20-poly1305@openssh.com MAC: <implicit> compression: none debug1: kex: client->server cipher: chacha20-poly1305@openssh.com MAC: <implicit> compression: none debug3: send packet: type 30 debug1: expecting SSH2_MSG_KEX_ECDH_REPLY debug3: receive packet: type 31 debug1: Server host key: ecdsa-sha2-nistp256 SHA256:FxFRdAJWsTnDQU0fif9sNEVRVnPbwfZcijrXAz153gk debug3: hostkeys_foreach: reading file "/home/nitin/.ssh/known_hosts" debug3: record_hostkey: found key type ECDSA in file /home/nitin/.ssh/known_hosts:7 debug3: load_hostkeys: loaded 1 keys from 15.214.245.237 debug1: Host '15.214.245.237' is known and matches the ECDSA host key. debug1: Found key in /home/nitin/.ssh/known_hosts:7 debug3: send packet: type 21 debug2: set_newkeys: mode 1 debug1: rekey after 134217728 blocks debug1: SSH2_MSG_NEWKEYS sent debug1: expecting SSH2_MSG_NEWKEYS debug3: receive packet: type 21 debug1: SSH2_MSG_NEWKEYS received debug2: set_newkeys: mode 0 debug1: rekey after 134217728 blocks debug2: key: /home/nitin/.ssh/id_rsa (0x7f4a7ce7e110), agent debug2: key: /home/nitin/.ssh/id_dsa ((nil)) debug2: key: /home/nitin/.ssh/id_ecdsa ((nil)) debug2: key: /home/nitin/.ssh/id_ed25519 ((nil)) debug3: send packet: type 5 debug3: receive packet: type 7 debug1: SSH2_MSG_EXT_INFO received debug1: kex_input_ext_info: server-sig-algs=<ssh-ed25519,ssh-rsa,rsa-sha2-256,rsa-sha2-512,ssh-dss,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521> debug3: receive packet: type 6 debug2: service_accept: ssh-userauth debug1: SSH2_MSG_SERVICE_ACCEPT received debug3: send packet: type 50 debug3: receive packet: type 51 debug1: Authentications that can continue: publickey,password,keyboard-interactive debug3: start over, passed a different list publickey,password,keyboard-interactive debug3: preferred publickey,keyboard-interactive,password debug3: authmethod_lookup publickey debug3: remaining preferred: keyboard-interactive,password debug3: authmethod_is_enabled publickey debug1: Next authentication method: publickey debug1: Offering RSA public key: /home/nitin/.ssh/id_rsa debug3: send_pubkey_test debug3: send packet: type 50 debug2: we sent a publickey packet, wait for reply debug3: receive packet: type 51 debug1: Authentications that can continue: publickey,password,keyboard-interactive debug1: Trying private key: /home/nitin/.ssh/id_dsa debug3: no such identity: /home/nitin/.ssh/id_dsa: No such file or directory debug1: Trying private key: /home/nitin/.ssh/id_ecdsa debug3: no such identity: /home/nitin/.ssh/id_ecdsa: No such file or directory debug1: Trying private key: /home/nitin/.ssh/id_ed25519 debug3: no such identity: /home/nitin/.ssh/id_ed25519: No such file or directory debug2: we did not send a packet, disable method debug3: authmethod_lookup keyboard-interactive debug3: remaining preferred: password debug3: authmethod_is_enabled keyboard-interactive debug1: Next authentication method: keyboard-interactive debug2: userauth_kbdint debug3: send packet: type 50 debug2: we sent a keyboard-interactive packet, wait for reply debug3: receive packet: type 51 debug1: Authentications that can continue: publickey,password,keyboard-interactive debug3: userauth_kbdint: disable: no info_req_seen debug2: we did not send a packet, disable method debug3: authmethod_lookup password debug3: remaining preferred: debug3: authmethod_is_enabled password debug1: Next authentication method: password
In future, please attach debug traces using the attachments feature. This is why your connection succeeds: debug1: kex: server->client cipher: chacha20-poly1305@openssh.com MAC: <implicit> compression: none debug1: kex: client->server cipher: chacha20-poly1305@openssh.com MAC: <implicit> compression: none chacha20-poly1305 and AES-GCM are AEAD ciphers that effectively include their own MAC. As such, the MAC you specified is ignored when they are selected. If you specify a plain confidentiality cipher (e.g. -c aes128-ctr) then your connection will fail as you expect.
cool. got ya. In file kex.c, below is the relevant code right ? authlen = cipher_authlen(newkeys->enc.cipher); /* ignore mac for authenticated encryption */ if (authlen == 0 && (r = choose_mac(ssh, &newkeys->mac, cprop[nmac], sprop[nmac])) != 0) { }
Yes, see also the PROTOCOL file: > AES-GCM is only negotiated as the cipher algorithms > "aes128-gcm@openssh.com" or "aes256-gcm@openssh.com" and never as > an MAC algorithm. Additionally, if AES-GCM is selected as the cipher > the exchanged MAC algorithms are ignored and there doesn't have to be > a matching MAC. and PROTOCOL.chacha20poly1305: > The chacha20-poly1305@openssh.com offers both encryption and > authentication. As such, no separate MAC is required. If the > chacha20-poly1305@openssh.com cipher is selected in key exchange, > the offered MAC algorithms are ignored and no MAC is required to be > negotiated.
Close all resolved bugs after release of OpenSSH 7.7.