Chinese Hackers Exploit Zero-Day Cisco Switch Flaw to Gain System Control

Details have emerged about a China-nexus threat group’s exploitation of a recently disclosed, now-patched security flaw in Cisco switches as a zero-day to seize control of the appliances and evade detection.

The activity, attributed to Velvet Ant, was observed early this year and involved the weaponization of CVE-2024-20399 (CVSS score: 6.0) to deliver bespoke malware and gain extensive control over the compromised system, facilitating both data exfiltration and persistent access.

“The zero-day exploit allows an attacker with valid administrator credentials to the Switch management console to escape the NX-OS command line interface (CLI) and execute arbitrary commands on the Linux underlying operating system,” cybersecurity company Sygnia said in a report shared with The Hacker News.

Velvet Ant first caught the attention of researchers at the Israeli cybersecurity company in connection with a multi-year campaign that targeted an unnamed organization located in East Asia by leveraging legacy F5 BIG-IP appliances as a vantage point for setting up persistence on the compromised environment.

The threat actor’s stealthy exploitation of CVE-2024-20399 came to light early last month, prompting Cisco to issue security updates to release the flaw.

Notable among the tradecraft are the level of sophistication and shape-shifting tactics adopted by the group, initially infiltrating new Windows systems before moving to legacy Windows servers and network devices in an attempt to fly under the radar.

“The transition to operating from internal network devices marks yet another escalation in the evasion techniques used in order to ensure the continuation of the espionage campaign,” Sygnia said.

The latest attack chain entails breaking into a Cisco switch appliance using CVE-2024-20399 and conducting reconnaissance activities, subsequently pivoting to more network devices and ultimately executing a backdoor binary by means of a malicious script.

The payload, dubbed VELVETSHELL, is an amalgamation of two open-source tools, a Unix backdoor named Tiny SHell and a proxy utility called 3proxy. It also supports capabilities to execute arbitrary commands, download/upload files, and establish tunnels for proxying network traffic.

“The modus-operandi of ‘Velvet Ant’ highlights risks and questions regarding third-party appliances and applications that organizations onboard,” the company said. “Due to the ‘black box’ nature of many appliances, each piece of hardware or software has the potential to turn into the attack surface that an adversary is able to exploit.”

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