Installing rogue firmware on embedded devices has long been a concern for security researchers, and it seems that such attacks have started to gain ground with hackers.
In an advisory Tuesday, Cisco Systems warned customers that it is aware of a limited number of cases where attackers have replaced the boot firmware on devices running its IOS operating system. IOS runs on most Cisco routers and switches and provides a complex set of networking tools and features.
Attackers used valid administrative credentials in order to replace the ROMMON image on IOS devices, Cisco said.
ROMMON, or ROM Monitor, is the low-level firmware responsible for initializing the hardware and booting up IOS. This means the attack is the equivalent of replacing the BIOS or UEFI (Unified Extensible Firmware Interface) on PCs with a malicious version.
"No product vulnerability is leveraged in this attack, and the attacker requires valid administrative credentials or physical access to the system to be successful," Cisco said in its advisory. "The ability to install an upgraded ROMMON image on IOS devices is a standard, documented feature that administrators use to manage their networks."
It's not clear how the attackers obtained the administrative credentials used in the ROMMON compromises seen by Cisco, but it should serve as a warning for companies with IOS equipment that network administrators are a target.
For attackers, the benefit of installing a malicious ROMMON image on a device is that it makes compromises persistent, as typical IOS infections don't survive across reboots.
Researchers have long highlighted the risk of attackers flashing rogue firmware on embedded devices in the absence of protections like encrypted and digitally signed updates. However, real-world attacks using this method have been rare until now.
Cisco first introduced a software digital signature verification feature in IOS Software Release 15.0(1)M for the Cisco 1900, 2900 and 3900 Series routers, as well as in IOS XE Release 3.1.0SG for Cisco Catalyst 4500 E-Series Switches.
To prevent, detect and remedy compromises of Cisco IOS devices, the company's product security incident response team advises customers to follow recommendations outlined in three documents: Cisco IOS Software Integrity Assurance, Cisco Guide to Harden IOS Devices and Telemetry-Based Infrastructure Device Integrity Monitoring.