Cisco Routers Compromised by Malicious Code Injection Attack

Fourteen Cisco routers in Ukraine, the Philippines, Mexico and India were implanted with malicious code by way of the new SYNful Knock attack, FireEye finds.


Hacking routers is a crime in most jurisdictions and, in at least 14 known cases around the world, it's also the result of a SYN (pronounced "sin"), which is a TCP packet synchronization component. In fact, FireEye's Mandiant division reported this week that it found at least 14 incidents in which a so-called "SYNful Knock" attack impacted Cisco routers in Ukraine, the Philippines, Mexico and India.

With the SYNful Knock, the default Cisco IOS router firmware is somehow replaced or tampered with, enabling an attacker to implant a backdoor. Cisco is already taking action to protect its customers and has published guidance on how to detect and mitigate the attack.

Mandiant found and reported the SYNful Knock attack to Cisco prior to publishing details about the vulnerability on Sept. 15.

"These attacks do not exploit vulnerabilities, but instead use compromised credentials or physical access to install malware on network devices," a Cisco spokesperson told eWEEK. "We've shared guidance on how customers can harden their network, and prevent, detect and remediate this type of attack. We thank Mandiant/FireEye for their additional focus on protecting our shared customers, and for adding their voice to calls for greater focus on network security."

While the SYNful Knock attack is first being reported against Cisco devices, it is not unique to anything specific that Cisco does on its hardware. FireEye is also emphasizing that the users didn't load a malicious firmware image on their own either.

"The attacker first compromised the router and then uploaded a modified router image to maintain persistence and gain additional capabilities," Tony Lee, technical director at FireEye, told eWEEK. "This was not the fault of the victims loading a bad image."

FireEye's research indicates that the router firmware implant provided unrestricted access using a secret backdoor password. Lee explained that rather than the backdoor password being hard-coded into the implant, FireEye's analysis is that the password can be modified and individualized on a per victim basis.

In many cases of infections, attackers seek to gather groups of assets and then make use of them by way of some form of coordinated command and control (C&C) technology. In the SYNful Knock attack, it's not clear if a controller is in place. Lee said that he was unable to comment whether or not FireEye detected a C&C node for the SYNful Knock attack.

From a technical perspective, once the SYNful Knock attacker enables an implant on a router, it is likely possible to exploit the router through multiple mechanisms, and not just by way of the TCP-SYN protocol.

"Any protocol or port could have been theoretically used," Lee said. "This is just the communication that the attacker chose to implement."

While Cisco is the only vendor mentioned in the FireEye Mandiant research, Lee emphasized that Cisco isn't the only vendor at risk.

"Every network vendor is at risk of the same attack," he said. "Cisco was most likely chosen because it is the biggest target and thus the attacker will have the highest return for their efforts."

Sean Michael Kerner is a senior editor at eWEEK and Follow him on Twitter @TechJournalist.

Sean Michael Kerner

Sean Michael Kerner

Sean Michael Kerner is an Internet consultant, strategist, and contributor to several leading IT business web sites.