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Attacks Exploiting VMware vSphere Flaw Spotted One Week After Patching

A critical vulnerability affecting VMware vCenter Server, the management interface for vSphere environments, is being exploited in the wild. Attacks started roughly a week after VMware announced the availability of patches.

In an advisory issued on May 25, VMware urged customers to immediately patch CVE-2021-21985 and warned that “the ramifications of this vulnerability are serious.”

VMware explained that the issue, discovered by Ricter Z of 360 Noah Lab, impacts the vSphere Client, specifically the Virtual SAN Health Check plugin, which is enabled by default in vCenter Server even if the plugin is not actually being used. An attacker with access to port 443 can exploit the flaw to execute commands with elevated privileges on the operating system that hosts vCenter Server.

A Chinese researcher who uses the online moniker “iswin” published a proof-of-concept (PoC) exploit on June 2. Threat intelligence firm Bad Packets reported seeing mass scanning activity targeting CVE-2021-21985 the next day.

Security researcher Kevin Beaumont also reported seeing scanning activity aimed at CVE-2021-21985 at around the same time, and on June 4 he confirmed that one of his honeypots was hacked.

VMware vCenter Server (CVE-2021-21985) exploited in the wild

Vietnamese security researcher Nguyen Jang has also released a PoC exploit, as well as technical details and a video showing the exploit in action. Ricter Z also detailed his findings on June 5. 

There are thousands of internet-exposed instances of vCenter Server.

“Don’t connect vCenter directly to the internet by design, especially the appliance version,” Beaumont warned. “The appliance version is closed box Linux with no AV; somebody drops a webshell on box and now it’s permanently backdoored (even if patched) with no way to know, and it has ESXi access.”

The U.S. Cybersecurity and Infrastructure Security Agency (CISA) also issued an alert to warn organizations about attacks targeting the vulnerability. 

This is not the first time threat actors have started exploiting a vCenter Server vulnerability shortly after it was patched. Earlier this year, scanning for systems impacted by CVE-2021-21972 began one day after fixes were released.

Cisco Talos reported last week that a piece of malware named Necro (aka Necromorph and FreakOut) has been exploiting CVE-2021-21972 since at least May. Necro is designed for DDoS attacks, network traffic exfiltration, and cryptocurrency mining.

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Eduard Kovacs (@EduardKovacs) is a contributing editor at SecurityWeek. He worked as a high school IT teacher for two years before starting a career in journalism as Softpedia’s security news reporter. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering.