I've applied this patch to Debian unstable (thanks!), so it'll be in
Ubuntu 17.04. I'd be happy to help somebody issue stable updates for
16.04 and 16.10, but am unlikely to have time to do that myself.
** Also affects: openssh (Ubuntu Yakkety)
Importance: Undecided
Status: New
** Also affects: openssh (Ubuntu Xenial)
Importance: Undecided
Status: New
** Changed in: openssh (Ubuntu Xenial)
Status: New => Triaged
** Changed in: openssh (Ubuntu Xenial)
Importance: Undecided => Medium
** Changed in: openssh (Ubuntu Yakkety)
Status: New => Triaged
** Changed in: openssh (Ubuntu Yakkety)
Importance: Undecided => Medium
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https://bugs.launchpad.net/bugs/1608965
Title:
ssh GSSAPI rekey failure
Status in openssh package in Ubuntu:
Triaged
Status in openssh source package in Xenial:
Triaged
Status in openssh source package in Yakkety:
Triaged
Bug description:
If I have ssh set up using GSSAPI with rekeying enabled, then the
connection fails on rekey, and tries to do host-based verification
'mid-session'.
Steps to reproduce:
$ ssh -vvv server.example.com
<snip...>
debug1: Authenticating to ssh.example.com:22 as 'user'
<snip...>
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
<snip...>
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
<snip...>
Last login: Tue Aug 02 10:47:20 2016 from foo
# Then do 'kinit' on the client to get a new ticket...
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:w7yxbCZNBX4d5EAgmCrFYa3XUpDjvWiDOw4/YOY9q8E
The authenticity of host 'server.example.com (10.0.0.1)' can't be established.
ECDSA key fingerprint is SHA256:w7yxbCZNBX4d5EAgmCrFYa3XUpDjvWiDOw4/YOY9q8E.
Are you sure you want to continue connecting (yes/no)?
Host key verification failed.
It looks like the list of KEX algorithms differs between the initial
connection, and the rekeying.
This behaviour seems to occur with a client running 16.04 (openssh-
client 1:7.2p2-4ubuntu1) but not on 15.10 (openssh-client
1:6.9p1-2ubuntu0.2).
ssh_config is as follows:
HashKnownHosts no
GSSAPIAuthentication yes
GSSAPIDelegateCredentials yes
GSSAPIRenewalForcesRekey yes
GSSAPITrustDNS yes
GSSAPIKeyExchange yes
ForwardX11 yes
ForwardX11Trusted yes
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