Short bio: Computer Scientist, FOSS supporter (read more)
Tux Machines (TM)-specific
My previous article in this series discussed SSH client security settings. To summarize, if you can’t control installations of rogue SSH clients, your only control is to limit outbound access through firewalling or other network-layer controls. Another of my articles discusses the issues with allowing outbound SSH access to the Internet.
SSH Servers: A Basic Risk Analysis
How do you secure your SSH servers? What are the total risks of such servers to your organization? You’re well aware of the possibility of people hacking your server and getting unauthorized access. That’s bad. But there are other risks. The SANS Institute’s Top 20 risk list really stresses SSH risks. If compromised, that host can be a router/forwarder that will forward any kind of traffic to any host the p0wned box can access—even your "secured" hosts given Internet Assigned Numbers Authority (IANA) reserved IP addresses. (Read RFC 3330 and RFC 1918 for the gory details on these addresses.) In most cases, those addresses aren’t accessible over the Internet.
More of a concern is your host’s threat to the rest of the Internet.