SSH Brute Force Attacks

SSH is used to establish secure connections across the internet. For example a lot of people use SSH to connect to their servers because of the good security it provides. Lots of people trust it and rely on it.

In the past week there has been a large increase in the number of brute force attacks against SSH. What’s a brute force attack? It’s when someone writes a program that starts guessing passwords. It’ll keep trying to guess passwords all day and all night without rest until it finds something that works. The smarter brute force attacks do this slowly so that servers don’t lock the account in defense.

To increase a hacker’s chances of finding the right password these brute force programs use a dictionary and try to guess common words first. Then they try combinations such as replacing o’s with zeros, or putting a 1 at the end (have you ever done this with passwords?). So if your password is based on a word found in the dictionary it’ll be amongst the first ones tried.

The best defence against brute force attacks is to use a complicated password. Complicated passwords can take years to guess, simple passwords can take seconds to guess. Read here about how to evaluate the complexity of a password. And if remembering complicated passwords is a challenge then you might need a password safe.

So back to SSH. If you manage a server and use SSH to connect to it, have a look at the logs. Other people have reported a 5-10 times increase in the number of SSH attempts on their servers. Make sure your passwords are complicated enough to resist brute force attacks. Consider editing firewall rules to limit the entry points into your network. And make sure everything is patched including routers and firewalls. See this article for further information on these attacks.

And for everything that’s still wondering what SSH is, don’t worry about the jargon. Just realise that people can and do try to guess passwords.

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