Package: openssh-client Version: 1:7.2p2-1 Severity: normal Dear Maintainer,
I get failures during rekey when using ssh with kerberos authentication and GSSAPI key-exchange. This can be noticed in long-running ssh sessions or when doing large scp transfers (or triggered manually in the ssh client, using the ~R escape sequence). As far as I can make out the ssh client offers a different set of key-exchange algorithms on initial connection and when doing the rekeying. Here is an example output: ------- $ ssh -vvv foo.example.com [...] debug1: Authenticating to foo.example.com:22 as 'user' [...] debug2: local client KEXINIT proposal debug2: KEX algorithms: gss-gex-sha1-toWM5Slw5Ew8Mqkay+al2g==,gss-group1-sha1-toWM5Slw5Ew8Mqkay+al2g==,gss-group14-sha1-toWM5Slw5Ew8Mqkay+al2g==,gss-gex-sha1-A/vxljAEU54gt9a48EiANQ==,gss-group1-sha1-A/vxljAEU54gt9a48EiANQ==,gss-group14-sha1-A/vxljAEU54gt9a48EiANQ==,gss-gex-sha1-bontcUwnM6aGfWCP21alxQ==,gss-group1-sha1-bontcUwnM6aGfWCP21alxQ==,gss-group14-sha1-bontcUwnM6aGfWCP21alxQ==,gss-gex-sha1-eipGX3TCiQSrx573bT1o1Q==,gss-group1-sha1-eipGX3TCiQSrx573bT1o1Q==,gss-group14-sha1-eipGX3TCiQSrx573bT1o1Q==,curve25519-sha...@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: peer server KEXINIT proposal debug2: KEX algorithms: gss-gex-sha1-toWM5Slw5Ew8Mqkay+al2g==,gss-group1-sha1-toWM5Slw5Ew8Mqkay+al2g==,gss-group14-sha1-toWM5Slw5Ew8Mqkay+al2g==,curve25519-sha...@libssh.org,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group14-sha1 [...] Last login: Fri Mar 25 09:56:20 2016 from foo foo% echo "now sending rekey request with ~R" now sending rekey request with ~R foo% debug1: need rekeying debug1: SSH2_MSG_KEXINIT sent debug1: rekeying in progress debug1: SSH2_MSG_KEXINIT received debug2: local client KEXINIT proposal debug2: KEX algorithms: curve25519-sha...@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 debug2: host key algorithms: ecdsa-sha2-nistp256-cert-...@openssh.com,ecdsa-sha2-nistp384-cert-...@openssh.com,ecdsa-sha2-nistp521-cert-...@openssh.com,ssh-ed25519-cert-...@openssh.com,ssh-rsa-cert-...@openssh.com,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,ssh-ed25519,rsa-sha2-512,rsa-sha2-256,ssh-rsa,null [...] debug2: peer server KEXINIT proposal debug2: KEX algorithms: gss-gex-sha1-toWM5Slw5Ew8Mqkay+al2g==,gss-group1-sha1-toWM5Slw5Ew8Mqkay+al2g==,gss-group14-sha1-toWM5Slw5Ew8Mqkay+al2g==,curve25519-sha...@libssh.org,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group14-sha1 [...] debug1: kex: algorithm: curve25519-sha...@libssh.org debug1: kex: host key algorithm: ecdsa-sha2-nistp256 debug1: kex: server->client cipher: chacha20-poly1...@openssh.com MAC: <implicit> compression: none debug1: kex: client->server cipher: chacha20-poly1...@openssh.com MAC: <implicit> compression: none debug1: expecting SSH2_MSG_KEX_ECDH_REPLY debug1: rekeying in progress debug1: rekeying in progress debug1: Server host key: ecdsa-sha2-nistp256 SHA256:w7yxbCZNBwQ0S0AgmCrFYa3XUpDjvWiDOw4/YOY9q8E The authenticity of host 'foo.example.com (10.0.1.2)' can't be established. ECDSA key fingerprint is SHA256:w7yxbCZNBwQ0S0AgmCrFYa3XUpDjvWiDOw4/YOY9q8E. Are you sure you want to continue connecting (yes/no)? Host key verification failed. ------- So it appears that the client does not see the gss-* methods but the server still does. / Peter -- System Information: Debian Release: stretch/sid APT prefers stable-updates APT policy: (500, 'stable-updates'), (500, 'testing') Architecture: amd64 (x86_64) Kernel: Linux 4.3.0-1-amd64 (SMP w/4 CPU cores) Locale: LANG=en_GB.UTF-8, LC_CTYPE=en_GB.UTF-8 (charmap=locale: Cannot set LC_ALL to default locale: No such file or directory UTF-8) Shell: /bin/sh linked to /bin/dash Init: systemd (via /run/systemd/system) Versions of packages openssh-client depends on: ii adduser 3.114 ii dpkg 1.18.4 ii libc6 2.22-3 ii libedit2 3.1-20150325-1+b1 ii libgssapi-krb5-2 1.13.2+dfsg-5 ii libselinux1 2.4-3+b1 ii libssl1.0.2 1.0.2g-1 ii passwd 1:4.2-3.1 ii zlib1g 1:1.2.8.dfsg-2+b1 Versions of packages openssh-client recommends: ii xauth 1:1.0.9-1 Versions of packages openssh-client suggests: pn keychain <none> pn libpam-ssh <none> pn monkeysphere <none> pn ssh-askpass <none> -- debconf information: