Attackers install highly persistent malware implants on Cisco routers

Replacing router firmware with poisoned versions is no longer just a theoretical risk. Researchers from Mandiant have detected a real-world attack that has installed rogue firmware on business routers in four countries.

The router implant, dubbed SYNful Knock, provides attackers with highly privileged backdoor access to the affected devices and persists even across reboots. This is different than the typical malware found on consumer routers, which gets wiped from memory when the device is restarted.

SYNful Knock is a modification of the IOS operating system that runs on professional routers and switches made by Cisco Systems. So far it was found by Mandiant researchers on Cisco 1841, 8211 and 3825 “integrated services routers,” which are typically used by businesses in their branch offices or by providers of managed network services.

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