Pierluigi Paganini February 04, 2023

A new wave of ransomware attacks is targeting VMware ESXi servers to deliver ransomware, CERT of France warns.

The French Computer Emergency Response Team (CERT-FR) warns that threat actors are targeting VMware ESXi servers to deploy ransomware.

CERT-FR reported that threat actors behind these ransomware attackers are actively exploiting the vulnerability CVE-2021-21974.

“OpenSLP as used in ESXi has a heap-overflow vulnerability.” reads the advisory published by VMware. “A malicious actor residing within the same network segment as ESXi who has access to port 427 may be able to trigger the heap-overflow issue in OpenSLP service resulting in remote code execution.”

The vulnerability is an OpenSLP heap-overflow flaw in VMware ESXi that can be exploited by attackers to execute arbitrary code remotely on vulnerable devices. The vulnerability affects the following systems:

• ESXi 7.x versions earlier than ESXi70U1c-17325551
• ESXi versions 6.7.x earlier than ESXi670-202102401-SG
• ESXi versions 6.5.x earlier than ESXi650-202102101-SG

The virtualization giant addressed the CVE-2021-21974 bug in February 2021.

“On February 3, 2023, CERT-FR became aware of attack campaigns targeting VMware ESXi hypervisors with the aim of deploying ransomware on them.” reads the alert published by CERT-FR. “In the current state of investigations , these attack campaigns seem to exploit the CVE-2021-21974 vulnerability, for which a patch has been available since February 23, 2021. This vulnerability affects the Service Location Protocol ( SLP ) service and allows a attacker to remotely exploit arbitrary code. The systems currently targeted would be ESXi hypervisors in version 6.x and prior to 6.7.”

CERT-FR urges applying all patches available for the ESXi hypervisor, it also recommends performing a system scan to detect any signs of compromise.

The CERT also recommends disabling the SLP service on ESXi hypervisors that have not been updated.

The ongoing ransomware attacks have been also reported by cloud service provider OVHcloud, which observed most of the attacks in Europe.

“A wave of attacks is currently targetting ESXi servers. No OVHcloud managed service are impacted by this attack however, since a lot of customers are using this operating system on their own servers, we provide this post as a reference in support to help them in their remediation.” reads the report published by OVH. “These attacks are detected globally and especially in Europe.”

According to experts, some of the attacks aimed at delivering the Nevada ransomware. Recently, researchers from cybersecurity firm Resecurity have identified a new version of Nevada Ransomware which recently emerged on the Dark Web right before the start of 2023.

Around February 1, 2023 – the group distributed an updated locker written in Rust for their affiliates supporting Windows, Linux and ESXi – this programming language has become a trend for ransomware developers these days (Blackcat, RansomExx2, Hive, Luna, Agenda).

However, BleepingComputer first reported that the attacks could be linked to a new ransomware family, tracked by ID Ransomware‘s Michael Gillespie as ESXiArgs.

The ransomware targets files with the .vmxf, .vmx, .vmdk, .vmsd, and .nvram extensions on compromised ESXi servers and creates a “.args” file for each encrypted document with metadata.

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Pierluigi Paganini

(SecurityAffairs – hacking, VMware ESXi servers)