Authenticated scan with special SSH options

Community Containers
1

Hello, I need to perform an authenticated scan for a legacy system that only supports SHA1 and RSA with a key length of 1024.

I use the latest Greenbone Community Containers in my setup. In the gvmd container the OpenSSH version 9.2 is installed:

root@de02ae653c95:/# ssh -V
OpenSSH_9.2p1 Debian-2+deb12u5, OpenSSL 3.0.15 3 Sep 2024

I added the file /etc/ssh/ssh_config.d/ssh_legacy.conf to the gvmd container in order to specify the SSH options for this connection:

Host 10.0.0.10
    HostKeyAlgorithms +ssh-rsa
    PubkeyAcceptedKeyTypes +ssh-rsa
    PubkeyAcceptedAlgorithms +ssh-rsa
    KexAlgorithms +diffie-hellman-group1-sha1
    RequiredRSASize 1024

After adding the conf file, I am able to connect via SSH in a bash session to the target system. However, when I trigger the authenticated scan via the web GUI, the SSH login attempt fails.

How can I modify the gvmd container in order to allow an ssh connection using the deprecated ssh algorithms mentioned above?

Thanks in advance!

BR,
Steffen

2

@hafnerst

It might be sensible to try, for example, an installation without containers — such as packaging for Kali Linux — since it’s more flexible in terms of customization.

Eero

3

Hello,

and welcome to this community forums. The scanner is not using OpenSSH but the libssh library from https://www.libssh.org/ so a lookup of the relevant documentation of that library might be required to determine the configuration support / options for these algorithms.

1 Like
4

Thanks for the link. I’lll check the libssh library.
Do you know which Docker container establishes the SSH connection for the authenticated scan to the target host?

Thank in advance!