China-linked APT exploited Cisco NX-OS zero-day to deploy custom malware

Cisco fixed an actively exploited NX-OS zero-day, the flaw was exploited to install previously unknown malware as root on vulnerable switches.

Cisco addressed an NX-OS zero-day, tracked as CVE-2024-20399 (CVSS score of 6.0), that the China-linked group Velvet Ant exploited to deploy previously unknown malware as root on vulnerable switches.

The flaw resides in the CLI of Cisco NX-OS Software, an authenticated, local attacker can exploit the flaw to execute arbitrary commands as root on the underlying operating system of an affected device.

“This vulnerability is due to insufficient validation of arguments that are passed to specific configuration CLI commands. An attacker could exploit this vulnerability by including crafted input as the argument of an affected configuration CLI command.” reads the advisory published by Cisco. “A successful exploit could allow the attacker to execute arbitrary commands on the underlying operating system with the privileges of root.”

The IT giant pointed out that only attackers with Administrator credentials can successfully exploit this vulnerability on a Cisco NX-OS device.

In April 2024, researchers reported to the Cisco Product Security Incident Response Team (PSIRT) that the issue was actively exploited in the wild.

Cybersecurity firm Sygnia observed the attacks on April 2024 and reported them to Cisco.

“Sygnia identified that CVE-2024-20399 was exploited in the wild by a China-nexus threat group as a ‘zero-day’ and shared the details of the vulnerability with Cisco. By exploiting this vulnerability, a threat group – dubbed ‘Velvet Ant’ – successfully executed commands on the underlying operating system of Cisco Nexus devices.” reads the report published by Sygnia. “This exploitation led to the execution of a previously unknown custom malware that allowed the threat group to remotely connect to compromised Cisco Nexus devices, upload additional files, and execute code on the devices.“

The vulnerability impacts the following devices:

• MDS 9000 Series Multilayer Switches (CSCwj97007)
• Nexus 3000 Series Switches (CSCwj97009)
• Nexus 5500 Platform Switches (CSCwj97011)
• Nexus 5600 Platform Switches (CSCwj97011)
• Nexus 6000 Series Switches (CSCwj97011)
• Nexus 7000 Series Switches (CSCwj94682) *
• Nexus 9000 Series Switches in standalone NX-OS mode (CSCwj97009)

Cisco recommends customers monitor the use of credentials for the administrative users network-admin and vdc-admin.

Cisco provides the Cisco Software Checker to help customers determine if their devices are vulnerable to this flaw.

In late 2023, Sygnia researchers responded to an incident suffered by a large organization that they attributed to the same China-linked threat actor ‘Velvet Ant.’

The cyberspies deployed custom malware on F5 BIG-IP appliances to gain persistent access to the internal network of the target organization and steal sensitive data.

Pierluigi Paganini

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(SecurityAffairs – hacking, NX-OS)