The threat actors behind the REvil ransomware gang appear to have pushed ransomware via an update for Kaseya's IT management software, hitting around 40 customers worldwide, in what's an instance of a widespread supply-chain ransomware attack.

"Beginning around mid-day (EST/US) on Friday, July 2, 2021, Kaseya's Incident Response team learned of a potential security incident involving our VSA software," the company's CEO Fred Voccola said in a statement shared late Friday.

Following the incident, the IT and security management services company said it took immediate steps to shut down our SaaS servers as a precautionary measure, in addition to notifying its on-premises customers to shut down their VSA servers to prevent them from being compromised.

Voccola also said the company has identified the source of the vulnerability and that it's readying a patch to mitigate the ongoing issues. In the interim, the company also noted it intends to keep all on-premise VSA servers, SaaS, and hosted VSA servers shut down until it's safe to resume operations.

According to Sophos Malware Analyst Mark Loman, the industry-wide supply chain attack leverages Kaseya VSA to deploy a variant of the REvil ransomware into a victim's environment, with the REvil binary side-loaded via a fake Windows Defender app to encrypt a victim's files.

The attack chain also involves attempts to disable Microsoft Defender Real-Time Monitoring via PowerShell, Loman added. The trojanized software is being distributed in the form of a "Kaseya VSA Agent Hot-fix," Huntress Labs said in a Reddit post detailing the workings of the breach.

The researchers noted they had found eight managed service providers (MSPs), companies that provide IT services to other companies, that had been hit by the attack. About 200 businesses that are served by these MSPs have been locked out of parts of their network, Huntress Labs said.

As the ransomware crisis continues to spiral, MSPs have emerged as a lucrative target, mainly because a successful break-in opens up access to multiple clients, making them all vulnerable at once.