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Unable to connect after applying the role (Ubuntu 18.04, AWS EC2) #229

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ghost opened this issue Jun 27, 2019 · 8 comments
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Unable to connect after applying the role (Ubuntu 18.04, AWS EC2) #229

ghost opened this issue Jun 27, 2019 · 8 comments
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@ghost
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ghost commented Jun 27, 2019

Describe the bug
A clear and concise description of what the bug is.

On AWS, I generate a fresh Uuntu 18.04 EC2 instance and provision it using Ansible. If The ssh-hardening role is used in the playbook, I get Connection closed when trying connecting after playbook installation. The connection is successful without the role.

Default roles values are used.

Expected behavior
A clear and concise description of what you expected to happen.

A successful connection.

Actual behavior

$ ssh -i ./ssh_private.pem -vvv ubuntu@XXX.XXX.XXX.XXX

OpenSSH_8.0p1, OpenSSL 1.1.1c FIPS  28 May 2019
debug1: Reading configuration data /home/fedora/.ssh/config
debug1: Reading configuration data /etc/ssh/ssh_config
debug3: /etc/ssh/ssh_config line 51: Including file /etc/ssh/ssh_config.d/05-redhat.conf depth 0
debug1: Reading configuration data /etc/ssh/ssh_config.d/05-redhat.conf
debug2: checking match for 'final all' host XXX.XXX.XXX.XXX originally XXX.XXX.XXX.XXX
debug3: /etc/ssh/ssh_config.d/05-redhat.conf line 3: not matched 'final'
debug2: match not found
debug3: /etc/ssh/ssh_config.d/05-redhat.conf line 5: Including file /etc/crypto-policies/back-ends/openssh.config depth 1 (parse only)
debug1: Reading configuration data /etc/crypto-policies/back-ends/openssh.config
debug3: gss kex names ok: [gss-gex-sha1-,gss-group14-sha1-,gss-group1-sha1-]
debug3: kex names ok: [curve25519-sha256,curve25519-sha256@libssh.org,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group14-sha256,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1]
debug1: configuration requests final Match pass
debug2: resolve_canonicalize: hostname XXX.XXX.XXX.XXX is address
debug1: re-parsing configuration
debug1: Reading configuration data /home/fedora/.ssh/config
debug1: Reading configuration data /etc/ssh/ssh_config
debug3: /etc/ssh/ssh_config line 51: Including file /etc/ssh/ssh_config.d/05-redhat.conf depth 0
debug1: Reading configuration data /etc/ssh/ssh_config.d/05-redhat.conf
debug2: checking match for 'final all' host XXX.XXX.XXX.XXX originally XXX.XXX.XXX.XXX
debug3: /etc/ssh/ssh_config.d/05-redhat.conf line 3: matched 'final'
debug2: match found
debug3: /etc/ssh/ssh_config.d/05-redhat.conf line 5: Including file /etc/crypto-policies/back-ends/openssh.config depth 1
debug1: Reading configuration data /etc/crypto-policies/back-ends/openssh.config
debug3: gss kex names ok: [gss-gex-sha1-,gss-group14-sha1-,gss-group1-sha1-]
debug3: kex names ok: [curve25519-sha256,curve25519-sha256@libssh.org,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group14-sha256,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1]
debug2: ssh_connect_direct
debug1: Connecting to XXX.XXX.XXX.XXX [XXX.XXX.XXX.XXX] port 22.
debug1: Connection established.
debug1: identity file ssh_private.pem type -1
debug1: identity file ssh_private.pem-cert type -1
debug1: Local version string SSH-2.0-OpenSSH_8.0
debug1: Remote protocol version 2.0, remote software version OpenSSH_7.6p1
debug1: match: OpenSSH_7.6p1 pat OpenSSH_7.0*,OpenSSH_7.1*,OpenSSH_7.2*,OpenSSH_7.3*,OpenSSH_7.4*,OpenSSH_7.5*,OpenSSH_7.6*,OpenSSH_7.7* compat 0x04000002
debug2: fd 4 setting O_NONBLOCK
debug1: Authenticating to XXX.XXX.XXX.XXX:22 as 'ubuntu'
debug3: hostkeys_foreach: reading file "/home/fedora/.ssh/known_hosts"
debug3: record_hostkey: found key type ECDSA in file /home/fedora/.ssh/known_hosts:37
debug3: load_hostkeys: loaded 1 keys from XXX.XXX.XXX.XXX
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-group14-sha256,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,diffie-hellman-group1-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,rsa-sha2-512-cert-v01@openssh.com,rsa-sha2-256-cert-v01@openssh.com,ssh-rsa-cert-v01@openssh.com,ssh-ed25519,rsa-sha2-512,rsa-sha2-256,ssh-rsa
debug2: ciphers ctos: aes256-gcm@openssh.com,chacha20-poly1305@openssh.com,aes256-ctr,aes256-cbc,aes128-gcm@openssh.com,aes128-ctr,aes128-cbc
debug2: ciphers stoc: aes256-gcm@openssh.com,chacha20-poly1305@openssh.com,aes256-ctr,aes256-cbc,aes128-gcm@openssh.com,aes128-ctr,aes128-cbc
debug2: MACs ctos: hmac-sha2-256-etm@openssh.com,hmac-sha1-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-sha2-256,hmac-sha1,umac-128@openssh.com,hmac-sha2-512
debug2: MACs stoc: hmac-sha2-256-etm@openssh.com,hmac-sha1-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-sha2-256,hmac-sha1,umac-128@openssh.com,hmac-sha2-512
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@libssh.org,diffie-hellman-group-exchange-sha256
debug2: host key algorithms: ssh-rsa,rsa-sha2-512,rsa-sha2-256,ecdsa-sha2-nistp256,ssh-ed25519
debug2: ciphers ctos: chacha20-poly1305@openssh.com,aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr,aes192-ctr,aes128-ctr
debug2: ciphers stoc: chacha20-poly1305@openssh.com,aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr,aes192-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
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
debug2: compression ctos: none
debug2: compression stoc: none
debug2: languages ctos:
debug2: languages stoc:
debug2: first_kex_follows 0
debug2: reserved 0
debug1: kex: algorithm: curve25519-sha256@libssh.org
debug1: kex: host key algorithm: ecdsa-sha2-nistp256
debug1: kex: server->client cipher: aes256-gcm@openssh.com MAC: <implicit> compression: none
debug1: kex: client->server cipher: aes256-gcm@openssh.com MAC: <implicit> compression: none
debug1: kex: curve25519-sha256@libssh.org need=32 dh_need=32
debug1: kex: curve25519-sha256@libssh.org need=32 dh_need=32
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:XXXXXXXXXXXXXXXXXXXXXXX
debug3: hostkeys_foreach: reading file "/home/fedora/.ssh/known_hosts"
debug3: record_hostkey: found key type ECDSA in file /home/fedora/.ssh/known_hosts:37
debug3: load_hostkeys: loaded 1 keys from XXX.XXX.XXX.XXX
debug1: Host 'XXX.XXX.XXX.XXX' is known and matches the ECDSA host key.
debug1: Found key in /home/fedora/.ssh/known_hosts:37
debug3: send packet: type 21
debug2: set_newkeys: mode 1
debug1: rekey out after 4294967296 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 in after 4294967296 blocks
debug1: Will attempt key: ssh_private.pem  explicit
debug2: pubkey_prepare: done
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
debug3: start over, passed a different list publickey
debug3: preferred gssapi-with-mic,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: Trying private key: ssh_private.pem
debug3: sign_and_send_pubkey: RSA SHA256:XXXXXXXXXXXXXXXXXXXXXXXXX
debug3: sign_and_send_pubkey: signing using rsa-sha2-256
debug3: send packet: type 50
debug2: we sent a publickey packet, wait for reply
Connection closed by XXX.XXX.XXX.XXX port 22

Example Playbook

- become: true
  hosts: all
  roles:
  - dev-sec.ssh-hardening

The playbook complete successfully.

OS / Environment

  • Client: Fedora 30 on AWS EC2 (AMI: Fedora-Cloud-Base-30-1.2.x86_64-hvm-eu-west-1-gp2-0 (ami-055eecae50058d2e0))
  • Server: Ubuntu 18.04 on AWS EC2 (AMI: ubuntu/images/hvm-ssd/ubuntu-bionic-18.04-amd64-server-20190617 (ami-08b1cea5487c762b3))

Ansible Version

ansible 2.8.1
  config file = /etc/ansible/ansible.cfg
  configured module search path = ['/home/fedora/.ansible/plugins/modules', '/usr/share/ansible/plugins/modules']
  ansible python module location = /usr/lib/python3.7/site-packages/ansible
  executable location = /usr/bin/ansible
  python version = 3.7.3 (default, May 11 2019, 00:38:04) [GCC 9.1.1 20190503 (Red Hat 9.1.1-1)]

It is the Ansible version from OS package ("ansible" 2.8.1-1.fc30)

Role Version

6.1.3

Additional context
Add any other context about the problem here.

SSH key: RSA 4096 with no password.
user: The default user for Ubuntu EC2 instances.
@rndmh3ro
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Hey @xlz-jgoutin,

the problem here is probably that the user ubuntu is not included in the ssh_allow_users-variable. Can you try this modified playbook and report back if it helps?

- become: true
  hosts: all
  vars:
    ssh_allow_users: 'ubuntu'
  roles:
  - dev-sec.ssh-hardening

@ghost
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ghost commented Jun 28, 2019

Hello,

I tried with your modified playbook but this does not solve the issue.

@timbroder

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@angrymeir

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@snoopotic
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Hi,
keep in mind that default of ssh_max_auth_retries: 2causes clients with more than one loaded identity file (ssh-add -l) that possibly only the third or fourth key would match the authorise_keys file on the server but this might be too late and that closes the connection.
Can you check this?
consider loading less keys in our client or raise the ssh_max_auth_retries value.
Does this help?

@chris-rock
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We started to allow overrides for max auth retries in dev-sec/ssh-baseline#138. We need to find a good default value that works for most cases.

I recommend that we continue with the ability to easily customize the value if the default is not working.

@ghost
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ghost commented Aug 27, 2019

I do not use the SSH agent and I specify the key to use directly (ssh -i ./ssh_private.pem).

Retested without success after confirming there are no identities in the agent:

$ ssh-add -l
The agent has no identities.

@rndmh3ro
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Duplicate of #189

@rndmh3ro rndmh3ro marked this as a duplicate of #189 Aug 31, 2019
@rndmh3ro rndmh3ro added the bug label Sep 17, 2019
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@timbroder @chris-rock @snoopotic @rndmh3ro @angrymeir