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Description of problem:
In FIPS mode, during DH group exchange, OpenSSH client should validate the received moduli, making sure it is one of the known groups.

Version-Release number of selected component (if applicable):
openssh-7.8p1

How reproducible:
100%

Steps to Reproduce:
1. Connect to the server using dh group exchange kex mechanism

Actual results:
The client will use one of the non-approved moduli sent by server

Expected results:
The client should make sure it is one of the known groups that are offered when the moduli file is missing

Additional info:
At this moment, OpenSSH server is sending either group14, group16 or group18, depending on the negotiated parameters, when the moduli file is not available.

Additionally, we should modify the server in the FIPS mode to ignore the /etc/moduli and use only the hardcoded modulis. It is less fragile than having the file removed or renamed in the crypto-policies FIPS setup.

The alternative is to disable the dh-group-exchange in the FIPS policy completely. We would lose the compatibility with RHEL-6 this way, on the other hand the compatibility is limited anyway as the RHEL-6 has to have the /etc/moduli file removed to send group14 and not some random prime from the moduli file.

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHSA-2019:3702