Cisco warns hackers are installing malicious ROMMON images on its devices

Cisco is warning enterprise customers about a spike in attacks in which hackers use valid admin credentials on IOS devices to install bogus ROMMON images.

Be aware network administrators, Cisco released a new Security Activity Bulletin referring a spike in attacks in which hackers use valid credentials on IOS devices to log in as administrators and then upload malicious ROMMON (IOS bootstrap) images to gain complete control of the devices

The ROM Monitor (ROMMON) is the program used to initialize the CISCO IOS devices, basically an attacker bu replacing it would have persistent access to the compromised device.

The attacker somehow accessed valid administrative credentials to access the CISCO devices, they aren’t exploiting any vulnerability, but experts speculate they are harvesting admin credentials to run the attacks and install the malicious ROMMON images.

“Cisco PSIRT has contacted customers to describe an evolution in attacks against Cisco IOS Classic platforms. Cisco has observed a limited number of cases where attackers, after gaining administrative or physical access to a Cisco IOS device, replaced the Cisco IOS ROMMON (IOS bootstrap) with a malicious ROMMON image,” states the advisory from Cisco.

“In all cases seen by Cisco, attackers accessed the devices using valid administrative credentials and then used the ROMMON field upgrade process to install a malicious ROMMON. Once the malicious ROMMON was installed and the IOS device was rebooted, the attacker was able to manipulate device behavior. Utilizing a malicious ROMMON provides attackers an additional advantage because infection will persist through a reboot.

 No product vulnerability is leveraged in this attack, and the attacker requires valid administrative credentials or physical access to the system to be successful. The ability to install an upgraded ROMMON image on IOS devices is a standard, documented feature that administrators use to manage their networks. No CVE ID will be assigned.”

Cisco will no assign any CVE ID, because there isn’t any vulnerability, hackers are exploiting a feature that Cisco implements, as many others network gear manufacturers do.

The problem here is how the attackers got the Admin credentials, but we cannot blame Cisco for this.

As usual let me suggest to adopt strong passwords, and keep them safe.

About the Author Elsio Pinto

Pierluigi Paganini

(Security Affairs – CISCO, ROMMON)