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[Dzivak <levanchuk@xxxxxx>]

** Also affects: openssh (openSUSE)
   Importance: Undecided
       Status: New

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https://bugs.launchpad.net/bugs/1350643

Title:
  6.2p1+ fails key-exchange with embedded SSH devices

Status in openssh package in Ubuntu:
  Triaged
Status in openssh package in openSUSE:
  New

Bug description:
  I have various network devices with embedded SSH daemons, such as
  CDUs, UPSs, managed Switches, DRAC, and so on. All devices have
  entries in the ssh config file specifying an IdentityFile.

  The particular embedded SSH daemon in this case is Mocana nanoSSH:

  http://www.mocana.com/for-device-manufacturers/nanossh

  Recently I had need to access a Server Technology Switched CDU via SSH
  using 14.04 Trusty and its OpenSSH_6.6.1p1. Connections consistently
  failed at:

  $ ssh -vvv cdu-01
  OpenSSH_6.6.1, OpenSSL 1.0.1f 6 Jan 2014
  debug1: Reading configuration data /home/tj/.ssh/config
  debug1: /home/tj/.ssh/config line 101: Applying options for cdu-01
  debug1: Reading configuration data /etc/ssh/ssh_config
  debug1: /etc/ssh/ssh_config line 19: Applying options for *
  debug1: Hostname has changed; re-reading configuration
  debug1: Reading configuration data /home/tj/.ssh/config
  debug1: Reading configuration data /etc/ssh/ssh_config
  debug1: /etc/ssh/ssh_config line 19: Applying options for *
  debug2: ssh_connect: needpriv 0
  debug1: Connecting to 10.254.0.3 [10.254.0.3] port 22.
  debug1: Connection established.
  ...
  debug2: kex_parse_kexinit: reserved 0
  debug2: mac_setup: setup hmac-md5
  debug1: kex: server->client aes128-cbc hmac-md5 none
  debug2: mac_setup: setup hmac-md5
  debug1: kex: client->server aes128-cbc hmac-md5 none
  debug2: bits set: 531/1024
  debug1: sending SSH2_MSG_KEXDH_INIT
  debug1: expecting SSH2_MSG_KEXDH_REPLY
  Received disconnect from 10.254.0.3: 11: Logged out.

  Initially I thought the local configuration had been corrupted in some
  way since the local /home/ was moved from a 13.04 to 14.04
  installation. Later I discovered a bug report of this issue affecting
  other embedded network devices reported against versions of OpenSSH
  later than 6.1p1 on the BSD operating system at:

  https://bugzilla.mindrot.org/show_bug.cgi?id=2116

  I then chroot-ed into the earlier 13.04 installation and tried again
  with its OpenSSH_6.1p1 and it connected:

  $ ssh -vvv hostmaster@10.254.0.3
  OpenSSH_6.1p1 Debian-4, OpenSSL 1.0.1c 10 May 2012
  debug1: Reading configuration data /etc/ssh/ssh_config
  debug1: /etc/ssh/ssh_config line 19: Applying options for *
  debug2: ssh_connect: needpriv 0
  debug1: Connecting to 10.254.0.3 [10.254.0.3] port 22.
  debug1: Connection established.
  ...
  debug2: kex_parse_kexinit: reserved 0
  debug2: mac_setup: found hmac-md5
  debug1: kex: server->client aes128-cbc hmac-md5 none
  debug2: mac_setup: found hmac-md5
  debug1: kex: client->server aes128-cbc hmac-md5 none
  debug2: dh_gen_key: priv key bits set: 117/256
  debug2: bits set: 521/1024
  debug1: sending SSH2_MSG_KEXDH_INIT
  debug1: expecting SSH2_MSG_KEXDH_REPLY
  debug1: Server host key: DSA 17:36:55:87:49:a5:a4:9f:02:42:8b:da:88:7c:bb:41
  The authenticity of host '10.254.0.3 (10.254.0.3)' can't be established.
  DSA key fingerprint is 17:36:55:87:49:a5:a4:9f:02:42:8b:da:88:7c:bb:41.
  Are you sure you want to continue connecting (yes/no)?

  The cause is apparently a buffer overflow in the embedded Mocana SSH
  daemon with cipher/mac lists longer than ~287 bytes.

  I fixed it by limiting the list of Ciphers and Macs sent, via the
  ssh_config:

  Host cdu-01
  Hostname 10.254.0.3
  User hostmaster
  IdentityFile ~/.ssh/id_hostmaster
  IdentitiesOnly yes
  Protocol 2
  Ciphers aes256-cbc,aes192-cbc,aes128-cbc,blowfish-cbc,3des-cbc,arcfour
  Macs hmac-sha1,hmac-md5

  
  $ ssh -vvv cdu-01  
  OpenSSH_6.6.1, OpenSSL 1.0.1f 6 Jan 2014
  debug1: Reading configuration data /home/tj/.ssh/config
  debug1: /home/tj/.ssh/config line 101: Applying options for cdu-01
  debug3: ciphers ok: [aes256-cbc,aes192-cbc,aes128-cbc,blowfish-cbc,3des-cbc,arcfour]
  debug3: macs ok: [hmac-sha1,hmac-md5]
  debug1: Reading configuration data /etc/ssh/ssh_config
  debug1: /etc/ssh/ssh_config line 19: Applying options for *
  debug1: Hostname has changed; re-reading configuration
  debug1: Reading configuration data /home/tj/.ssh/config
  debug3: ciphers ok: [aes256-cbc,aes192-cbc,aes128-cbc,blowfish-cbc,3des-cbc,arcfour]
  debug3: macs ok: [hmac-sha1,hmac-md5]
  debug1: Reading configuration data /etc/ssh/ssh_config
  debug1: /etc/ssh/ssh_config line 19: Applying options for *
  debug2: ssh_connect: needpriv 0
  debug1: Connecting to 10.254.0.3 [10.254.0.3] port 22.
  debug1: Connection established.
  ...
  debug1: sending SSH2_MSG_KEXDH_INIT
  debug1: expecting SSH2_MSG_KEXDH_REPLY
  debug1: Server host key: DSA 17:36:55:87:49:a5:a4:9f:02:42:8b:da:88:7c:bb:41
  debug3: load_hostkeys: loading entries for host "10.254.0.3" from file "/home/tj/.ssh/known_hosts"
  debug3: load_hostkeys: loaded 0 keys
  The authenticity of host '10.254.0.3 (10.254.0.3)' can't be established.
  DSA key fingerprint is 17:36:55:87:49:a5:a4:9f:02:42:8b:da:88:7c:bb:41.
  Are you sure you want to continue connecting (yes/no)?

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