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Brutish SSH attacks continue to bear fruit

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The number of attacks against secure shells protecting Linux boxes, internet routers and other network devices has continued to climb over the past several years, an indication that they still bear fruit for the miscreants who mount them.

Data collected by DShield.org, a organization that aggregates firewall logs from across the planet, shows no abatement in brute-force password attacks for secure shell, or SSH, devices. Those attacks work by submitting several dozen to several hundred combinations of user names and passwords to SSH-enabled devices connected to the internet. Even a tiny percentage of successes can prove valuable if the attacks are sufficiently widespread.

"This particular attack is high volume, low impact," said John Bambenek, a handler at the Sans Internet Storm Center, who has been crunching the numbers and reading the logs. "People are not spending a lot of time to break in. They're looking for low-hanging fruit."

Translation: the reason the attempts to crack SSH passwords continues is that enough of them succeed to justify the expense.

SSH is used to create an encrypted channel so administrators can transfer files or execute shell commands on a remote server or network device. Gain access to an SSH account and there's a fair chance you'll get your hands on all kinds of sensitive resources. Bots that perform the scans are often equipped with tools that automate privilege escalation once an SSH account has been breached.

Witness this post from fellow Sans handler Daniel Wesemann from last month that recounts one successful attack against a poorly protected Cisco router. After correctly guessing the SSH password for a user account called test, the attacker was able to use it to tunnel back to the home base.

The proliferation of the attacks comes as more and more newbies use Linux and network devices designed to offer out-of-the-box SSH deployments.

"There used to be a point when people who were using SSH were fairly security savvy," said Bambenek. "I'm not sure that's the case anymore. They use SSH boxes and think just by having it there they're safe."

The reality is a bit more complicated. Rule number one: as with other services such as FTP, if you don't use it, don't enable it. Sans offers other SSH security tips here. More are available here from CentOS. ®

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