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Operating Systems Solaris Change from weak ssh host key to strong one Post 303036682 by rbatte1 on Monday 8th of July 2019 05:35:10 AM
Old 07-08-2019
Just came across this. One thing to be aware of is that all clients will object when you next try to connect them. They will alert on there being a possible man-in-the-middle attack or a DNS attack that is trying to send you to a different host (as determined by the keys) so you would need to get each client to forget the server keys for the machine(s) you are replacing the keys on and re-validate them all, or manually replace the old key with the new on all the clients.

You need to consider all the names that the clients could refer to the server as, be that IP, local hosts, DNS short name, fully qualified DNS name, DNS alias etc. and look for those in ~/.ssh/known_hosts

You will need to do this for every account on every client, so it is not a thing to be done lightly, especially if there are multiple automated jobs that connect with SSH, SCP, SFTP etc. that you need to ensure are not disrupted.


Sorry if I've made you panic, but better that than a massive failure.



I hope that this helps,
Robin
 

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ssh-keysign(1M) 														   ssh-keysign(1M)

NAME
ssh-keysign - ssh helper program for host-based authentication SYNOPSIS
ssh-keysign ssh-keysign is used by ssh(1) to access the local host keys and generate the digital signature required during host-based authentication with SSH protocol version 2. This signature is of data that includes, among other items, the name of the client host and the name of the client user. ssh-keysign is disabled by default and can be enabled only in the global client configuration file /etc/ssh/ssh_config by setting Host- basedAuthentication to yes. ssh-keysign is not intended to be invoked by the user, but from ssh. See ssh(1) and sshd(1M) for more information about host-based authen- tication. /etc/ssh/ssh_config Controls whether ssh-keysign is enabled. /etc/ssh/ssh_host_dsa_key /etc/ssh/ssh_host_rsa_key These files contain the private parts of the host keys used to generate the digital signature. They should be owned by root, readable only by root, and not accessible to others. Because they are readable only by root, ssh-keysign must be set-uid root if host-based authentication is used. ssh-keysign will not sign host-based authentication data under the following conditions: o If the HostbasedAuthentication client configuration parameter is not set to yes in /etc/ssh/ssh_config. This setting cannot be overri- den in users' ~/.ssh/ssh_config files. o If the client hostname and username in /etc/ssh/ssh_config do not match the canonical hostname of the client where ssh-keysign is invoked and the name of the user invoking ssh-keysign. In spite of ssh-keysign's restrictions on the contents of the host-based authentication data, there remains the ability of users to use it as an avenue for obtaining the client's private host keys. For this reason host-based authentication is turned off by default. See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Availability |SUNWsshu | +-----------------------------+-----------------------------+ |Interface Stability |Evolving | +-----------------------------+-----------------------------+ ssh(1), sshd(1M), ssh_config(4), attributes(5) AUTHORS
Markus Friedl, markus@openbsd.org HISTORY
ssh-keysign first appeared in Ox 3.2. 9 Jun 2004 ssh-keysign(1M)
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