Cisco SMI Still Exposing Network Switches Online

Cisco's Smart Install (SMI) protocol is leaving network switches exposed on the public Internet at a rate that has remained largely unchanged since researchers began digging for SMI flaws when it was first released in 2010, a new study shows.

SMI provides configuration and image management for Cisco switches and uses a combination of DHCP, TFTP, and a proprietary TCP protocol to help businesses deploy and run them.

Researchers at Rapid7 recently reassessed the public Internet for SMI exposure. Their goal was to highlight changes since the initial publication of SMI research and learn more about why SMI was being exposed insecurely.

Since its debut, several SMI flaws have been discovered and disclosed including CVE-2011-3271, which led to remote code execution, and denial of service issues CVE-2012-0385, CVE-2013-1146, CVE-2016-1349, and CVE-2016-6385.

In 2016, researchers have found a number of new SMI security issues. Experts from Tenable, Trustwave SpiderLabs, and Digital Security presented at the 2016 Zeronights security conference to disclose several problems with SMI that left the entire switch open for compromise if a user left SMI exposed and unpatched, neglecting Cisco's recommendations for securing it.

Each SMI-related security advisory published by Cisco has recommended disabling SMI unless it's needed. The company has offered coverage for SMI abuse, updated the documentation to secure SMI, and released a scanning tool so customers can know if they're affected by SMI problems. It also released SMI-related hardening fixes.

In its new July 2017 reassessment of the public Internet, Rapid7 used a method similar to Zeronights. The Rapid7 Labs' Sonar scan found a 13% decrease in the number of exposed SMI endpoints compared with the Zeronights research. Countries with a large number of IPv4 IPs and large network infrastructure are the most exposed. The United States was highest with 56,605 nodes exposed, or 26.3% of the total.

"The issue with exposing SMI is that it gives an attacker complete control over the configuration of the target switch," says Jon Hart, senior security researcher at Rapid7. At the minimum, he explains, there is the possibility of information disclosure, which is likely to include authentication data like usernames, passwords/hashes, firewall/ACL rules, and more.

On the more extreme end, he continues, SMI exposure could let an attacker completely compromise the target switch and load arbitrary switch operating system code. They could execute code of their choosing and modify, redirect, or intercept switch transit traffic.

"Compromising a switch puts an attacker in a very advantageous position offensively," says Hart. "Being closer network-wise to additional target devices that connect to or through the compromised switch affords an attacker the ability to perform attacks against these additional targets."

Businesses can protect themselves by updating to newer versions of the relevant code powering these switches, which will likely remove any current risk of being compromised via SMI, he says. It's an improvement from several years ago, when organizations could have been running and exposing SMI without knowing it.

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