How to disable strict host key checking in ssh?

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By default, the SSH client verifies the identity of the host to which it connects.

If the remote host key is unknown to your SSH client, you would be asked to accept it by typing "yes" or "no".

This could cause a trouble when running from script that automatically connects to a remote host over SSH protocol.

This article explains how to bypass this verification step by disabling host key checking.

The Authenticity Of Host Can't Be Established

When you log into a remote host that you have never connected before, the remote host key is most likely unknown to your SSH client, and you would be asked to confirm its fingerprint:

The authenticity of host ***** can't be established. RSA key fingerprint is *****. Are you sure you want to continue connecting (yes/no)?

If your answer is yes, the SSH client continues login, and stores the host key locally in the file ~/.ssh/known_hosts.

If you would like to bypass this verification step, you...

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When you connect to a ssh server for the first time, you will be shown a fingerprint, a hash of its full host key, and asked to confirm its validity, and accept the host key. Once confirmed, the host key will be added to ~/.ssh/known_hosts file. However, in a controlled environment where the authenticity of ssh hosts is already known, you may want to automatically accept a new host key without checking. This will be useful when you ssh/scp in a non-interactive batch processing script.

In this post, I will describe how to automatically accept ssh host keys on Linux.

The ssh command allows you to use "-oStrictHostKeyChecking=[yes|no]" command line option to enable or disable ssh host key checking. To ssh without strict host key checking, run the following.

$ ssh -oStrictHostKeyChecking=no user@remote_host

In this case, you will not be prompted to accept a host key. Note that you may still see "WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED"...

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Answer #: 1

In your ~/.ssh/config (if this file doesn’t exist, just create it):

Host * StrictHostKeyChecking no

This will turn it off for all hosts you connect to. You can replace the * with a hostname pattern if you only want it to apply to some hosts.

Answer #: 2

Rather than adding it to your ~/.ssh/config file for all Host *, it would be a safer to specify a particular host.

You can also pass a parameter on the command-line like this:

ssh -o StrictHostKeyChecking=no yourHardenedHost.com

Answer #: 3

I don’t have the rep yet to comment above – but it’s worth pointing out:

StrictHostKeyChecking no

Will mean hostkeys are still added to .ssh/known_hosts – you just won’t be prompted about whether you trust them, but should hosts change I’m willing to bet you’ll get the big warning about it. You can work around this problem by adding another parameter:

UserKnownHostsFile /dev/null

This will add all these “newly...

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Posted on March 12, 2009. Filed under: Linux, Services, Windows |

Remote login using the SSH protocol is a frequent activity in today’s internet world. With the SSH protocol, the onus is on the SSH client to verify the identity of the host to which it is connecting. The host identify is established by its SSH host key. Typically, the host key is auto-created during initial SSH installation setup.

By default, the SSH client verifies the host key against a local file containing known, rustworthy machines. This provides protection against possible Man-In-The-Middle attacks. However, there are situations in which you want to bypass this verification step. This article explains how to disable host key checking using OpenSSH, a popular Free and Open-Source implementation of SSH.

When you login to a remote host for the first time, the remote host’s host key is most likely unknown to the SSH client. The default behavior is to ask the user to confirm the fingerprint of...

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SSH to server with multiple keys while retaining strict checking

location: ubuntuforums.com - date: November 28, 2009
OK, so my university's server has ssh, but with multiple rotating RSA keys. You guessed it. I'm hitting the DNS SPOOFING warning. I'd like to retain strict checking. Assuming I get them in xxxxxx... format, what do I use to generate the appropriate entries in my known_hosts file?

SSH/Telnet, disable root login, how?

location: linuxquestions.com - date: October 6, 2003
Hi, We have an amature group of Linux admin, and we recently had a break into our Linux system - and we have just re-install everything. We have a reverse problem however (unlike Goma_2's). We are currently able to login as root via telnet or ssh. How do we disable it ? And how do we disable root login directly at the terminal ? We remember that we managed to have a configuration where root cannot login directly at the ternimal or remote. But we also set a 'special' user that...

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Remote login using the

SSH

protocol is a frequent activity in today's internet world. With the SSH protocol, the onus is on the SSH client to verify the identity of the host to which it is connecting. The host identify is established by its SSH host key. Typically, the host key is auto-created during initial SSH installation setup.

By default, the SSH client verifies the host key against a local file containing known, trustworthy machines. This provides protection against possible Man-In-The-Middle attacks. However, there are situations in which you want to bypass this verification step. This article explains how to disable host key checking using OpenSSH, a popular Free and Open-Source implementation of SSH.

When you login to a remote host for the first time, the remote host's host key is most likely unknown to the SSH client. The default behavior is to ask the user to confirm the fingerprint of the host key.

$ ssh [email protected]
The...
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I‘ve a remote Unix server running with OpenSSH remote login service. The openssh is configured for passwordless login using ssh keys. Our ISP allows to boot all Linux servers into the rescue mode. It allow us to bring a server online remotely in order to troubleshoot system problems that would normally only be resolved by an OS Reload (such as accidentally deleting files or wrong firewall configurations blocking ssh access). When server boots into a remote rescue mode I can connect using SSH. They SSH keys will not be the same in the rescue mode so I get key mismatch messages as SSH keys are re-generated on each boot:

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that the RSA host key has just been changed.
The...

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Quelle: http://linuxcommando.blogspot.co.at/2008/10/how-to-disable-ssh-host-key-checking.html

Remote login using the SSH protocol is a frequent activity in today’s internet world. With the SSH protocol, the onus is on the SSH client to verify the identity of the host to which it is connecting. The host identify is established by its SSH host key. Typically, the host key is auto-created during initial SSH installation setup.

By default, the SSH client verifies the host key against a local file containing known, trustworthy machines. This provides protection against possible Man-In-The-Middle attacks. However, there are situations in which you want to bypass this verification step. This article explains how to disable host key checking using OpenSSH, a popular Free and Open-Source implementation of SSH.

When you login to a remote host for the first time, the remote host’s host key is most likely unknown to the SSH client. The default behavior is to ask the user...

0 0
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Those of you new to Internet of Things (IoT) engineering and using boards such as the Raspberry Pi will probably have come across an irritation: Every time you wipe the operating system on your IoT device and then try to use the Secure Shell (SSH) to access it, SSH will complain with something along the lines of:

RedQueen:~ mgibbs$ ssh pi@192.168.0.37

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@

@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@

IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!

Someone could be eavesdropping on you right now (man-in-the-middle attack)!

It is also possible that a host key has just been changed.

The fingerprint for the ECDSA key sent by the remote host is

SHA256:X0L/BQW/2WvWKnkIAsRGcSr41Hsw/uVffWkP7bLFUuo.

Please contact your system administrator.

Add correct host key in...

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Before you generate an SSH key, you can check to see if you have any existing SSH keys.

Open TerminalTerminalGit Bash.

Enter ls -al ~/.ssh to see if existing SSH keys are present:

ls -al ~/.ssh # Lists the files in your .ssh directory, if they exist

Check the directory listing to see if you already have a public SSH key.

By default, the filenames of the public keys are one of the following:

id_dsa.pub id_ecdsa.pub id_ed25519.pub

id_rsa.pub

If you don't have an existing public and private key pair, or don't wish to use any that are available to connect to GitHub, then generate a new SSH key.

If you see an existing public and private key pair listed (for example id_rsa.pub and id_rsa) that you would like to use to connect to GitHub, you can add your SSH key to the ssh-agent.

Tip: If you receive an error that ~/.ssh doesn't exist, don't worry! We'll create it when we generate a new SSH...

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Now that you’ve read Installation and installed Ansible, it’s time to dig in and get started with some commands.

What we are showing first are not the powerful configuration/deployment/orchestration features of Ansible. These features are handled by playbooks which are covered in a separate section.

This section is about how to initially get going. Once you have these concepts down, read Introduction To Ad-Hoc Commands for some more detail, and then you’ll be ready to dive into playbooks and explore the most interesting parts!

Before we get started, it’s important to understand how Ansible communicates with remote machines over SSH.

By default, Ansible 1.3 and later will try to use native OpenSSH for remote communication when possible. This enables ControlPersist (a performance feature), Kerberos, and options in ~/.ssh/config such as Jump Host setup. However, when using Enterprise Linux 6 operating systems as the control machine (Red Hat Enterprise Linux...

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[Virt-test-devel] [PATCH] Disable strict host key checking for ssh [Date Prev][Date Next] [Thread Prev][Thread Next] [Thread Index] [Date Index] [Author Index] From: Lin Ma To: virt-test-devel redhat com Subject: [Virt-test-devel] [PATCH] Disable strict host key checking for ssh Date: Tue, 25 Feb 2014 22:07:53 +0800 The tests which containing ssh session will be blocked by host key checking if the incoming ssh host keys are not listed in known_hosts file of guest, So disable the checking. Signed-off-by: Lin Ma --- virttest/remote.py | 4 ++++ virttest/utils_env.py | 1 + 2 files changed, 5 insertions(+) diff --git a/virttest/remote.py b/virttest/remote.py index 66cb26e..99a3f6e 100644 --- a/virttest/remote.py +++ b/virttest/remote.py @@ -207,6 +207,7 @@ def remote_login(client, host, port, username, password, prompt, linesep="\n", """ if client == "ssh": cmd = ("ssh -o UserKnownHostsFile=/dev/null " + "-o StrictHostKeyChecking=no " "-o...
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It's worth pointing out that:

StrictHostKeyChecking no

Will mean hostkeys are still added to .ssh/known_hosts - you just won't be prompted about whether you trust them, but should hosts change I'm willing to bet you'll get the big warning about it. You can work around this problem by adding another parameter:

UserKnownHostsFile /dev/null

This will add all these "newly discovered" hosts to the trash bin. If a host key changes, no troubles.

I would be remiss not to mention that circumventing these warnings on hostkeys has obvious security ramifications - you should be careful that you're doing it for the right reasons & that what you're connecting to actually is what you mean to connect to and not a malicious...

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Remote login using the SSH protocol is a common activity in my line of work. With the SSH protocol, the responsibility is on the SSH client to verify the identity of the host to which it is connecting. The host identify is established by its SSH host key. Typically, the host key is auto-created during initial SSH installation setup.

By default, the SSH client verifies the host key against a local file containing known, rustworthy machines. This provides protection against possible Man-In-The-Middle attacks. However, there are situations in which you want to bypass this verification step. This article explains how to disable host key checking using OpenSSH, a popular Free and Open-Source implementation of SSH.

When you login to a remote host for the first time, the remote host's host key is most likely unknown to the SSH client. The default behavior is to ask the user to confirm the fingerprint of the host key.

$ ssh erik@192.168.0.100
The authenticity of...

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This is the first in a series of articles on SSH in-depth. We start with looking at standard SSH host keys by examining the verification process to ensure you have not been the victim of an attack. Please note that this article applies to the widely used OpenSSH application that is bundled with most Unix based operating systems, and not the commercial version of SSH.

SSH Host Keys as a protection against Man-In-The-Middle Attacks

SSH is a ubiquitous protocol that offers secure, encrypted connections for a variety of purposes, including logging into remote machines, transferring files, setting up encrypted tunnels, running remote commands without manual authentication, and more. It was created to replace many non-encrypted protocols such as Telnet, FTP, RSH, and the like.

One of the problems with these old protocols, aside from the fact that they send everything (your password included) in the clear, is that they are vulnerable to man-in-the-middle attacks....

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ssh - OpenSSH SSH client (remote login program) ssh [-1246AaCfgkMNnqsTtVvXxY] [-b bind_address] [-c cipher_spec] [-D
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.Ek ssh (SSH client) is a program for logging into a remote machine and for executing commands on a remote machine. It is intended to replace rlogin and rsh, and provide secure encrypted communications between two untrusted hosts over an insecure network. X11 connections and arbitrary TCP ports can also be forwarded over the secure channel.

ssh connects and logs into the specified hostname (with...

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H

ow do I regenerate OpenSSH sshd server host keys stored in /etc/ssh/ssh_host_* files? Can I safely regenerate ssh host keys using remote ssh session as my existing ssh connections shouldn’t be interrupted on Debian or Ubuntu Linux?


To regenerate keys you need to delete old files and reconfigure openssh-server. It is also safe to run following commands

over remote ssh based session

. Your

existing session shouldn’t be interrupted

.

Step # 1: Delete old ssh host keys

Login as the root and type the following command to delete files on your SSHD server:
# /bin/rm -v /etc/ssh/ssh_host_*

Step # 2: Reconfigure OpenSSH Server

Now create a new set of keys on your SSHD server, enter:
# dpkg-reconfigure openssh-server
Sample output:

Creating SSH2 RSA key; this may take some time ... Creating SSH2 DSA key; this may take some time ... Restarting OpenBSD Secure Shell server: sshd.

Step # 3: Update all ssh...

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W

hen I run ssh command I get an error which read as follows:

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that the RSA host key has just been changed.
The fingerprint for the RSA key sent by the remote host is
5c:9b:16:56:a6:cd:11:10:3a:cd:1b:a2:91:cd:e5:1c.
Please contact your system administrator.
Add correct host key in /home/user/.ssh/known_hosts to get rid of this message.
Offending key in /home/user/.ssh/known_hosts:1
RSA host key for ras.mydomain.com has changed and you have requested strict checking.
Host key verification failed.

How do I get rid of this message?

If you have reinstalled Linux or UNIX server with OpenSSH, you will get the above error from client...

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