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Cisco Warns of Possible Smart Install Client Hacking

Following an alert by US-CERT about possible hacking by foreign governments, Cisco is warning customers about a port vulnerability in the company's legacy Smart Install Client.

Larry Loeb

April 9, 2018

4 Min Read

In March, the US Computer Emergency Readiness Team (US-CERT) issued an unprecedented alert about Russian hacking of industrial control systems, especially in the energy sector.

Done in conjunction with the US Department of Homeland Security and the FBI, the CERT alert did not specify exactly how this was all happening. However, the details are now seeping out. (See FBI & DHS Accuse Russia of Hacking Critical Infrastructure.)

Cisco Talos has found evidence of attempts to attack Cisco switches that are used in infrastructure installations that fit the profile CERT warned about. Groups such as Dragonfly, Crouching Yeti and Energetic Bear are linked to the attacks, with Dragonfly seemingly the main perpetrator.

(Source: Wikimedia)

(Source: Wikimedia)

The attacks are focused on the Cisco Smart Install (SMI) Client, legacy utility. When it was originally released -- in a time that had differing threat models and IT didn't consider someone hacking the switch – the client allowed for the no-touch installation of Cisco switches. It has since been superseded by the Cisco Network Plug and Play solution.

But when end-users install the switch with the new method, they did not configure or disable the obsolete Smart Install protocol. So, the client will still be listening in the background for the "installation/configuration" commands that it expects.

In its report, Cisco noted that the protocol: "can be abused to modify the TFTP server setting, exfiltrate configuration files via TFTP, modify the configuration file, replace the IOS image, and set up accounts, allowing for the execution of IOS commands."

In February 2017, Cisco first issued an advisory about misuse of the protocol. It's not a new issue.

What is new, however, is the increase in Shodan scans for port 4786 -- the port used in exploiting SMI -- which has occurred since the company first issued an advisory. Cisco reports that there are 168,000 SMI-enabled Cisco switches left exposed, which is less than the 251,000 that were observed in 2016.

However, there are reports that a hacker group calling itself "JHT" used this exploit over this weekend to nail Russian and Iranian networks that were subject to the vulnerability. Reports indicated that 3,500 of the affected switches were in Iran. The attack affected Internet service providers and reportedly cut off web access for their subscribers.

This situation differs from the vulnerability that was recently found by Embedi in the Smart Install client. In that case, a specially crafted malicious message can cause a stack-based buffer overflow. Cisco has issued a patch for it, but it does not directly relate to the protocol misuse issue that Cisco is once again discussing.

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There are a few mitigation paths here.

Cisco has released an open source tool to scan and check if the protocol is still present in switch installations. There is also a Snort path (SID: 41722-41725) to detect any attempts to leverage this type of technology.

Additionally Cisco advises removal of the Smart Install Client from all devices where it is not used. To remove the Smart Install, Cisco recommends running the no vstack command on the switch. If that isn't possible, then an access control list can be implemented to limit access to specified hosts.

Switches are building blocks of control systems, and can cause great damage if misused. It is refreshing to see Cisco emphasize solutions to what could be a dangerous problem.

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— Larry Loeb has written for many of the last century's major "dead tree" computer magazines, having been, among other things, a consulting editor for BYTE magazine and senior editor for the launch of WebWeek.

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About the Author(s)

Larry Loeb

Blogger, Informationweek

Larry Loeb has written for many of the last century's major "dead tree" computer magazines, having been, among other things, a consulting editor for BYTE magazine and senior editor for the launch of WebWeek. He has written a book on the Secure Electronic Transaction Internet protocol. His latest book has the commercially obligatory title of Hack Proofing XML. He's been online since uucp "bang" addressing (where the world existed relative to !decvax), serving as editor of the Macintosh Exchange on BIX and the VARBusiness Exchange. His first Mac had 128 KB of memory, which was a big step up from his first 1130, which had 4 KB, as did his first 1401. You can e-mail him at [email protected].

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