Large organizations may be targeted by “big game ransomware” if they risk leaving a vulnerability in Pulse Secure virtual private network (VPN) servers unpatched, a cybersecurity researcher warned.

In a post on his Double Pulsar blog, Kevin Beaumont said the problem stems from April of last year when Pulse Secure issued an important fix to a problem in one of its VPN products, Zero Trust.

The vulnerability could allow attackers to view logs remotely after connecting to networks and even bypass multifactor authentication (MFA). Examples of the so-called big game ransomware that could be used included REvil, also known as Sodinokibi.

Exposure via Shodan

Organizations that haven’t gotten around to patching systems may hope they’re simply overlooked by cybercriminals. That kind of bet could backfire in this case, however. Vulnerable Pulse VPN servers can easily be identified through a search engine known as Shodan.io, the researcher said.

Rogue actors don’t even need valid credentials to conduct attacks using REvil, the report added. Instead, once they’ve gained access, they can grab admin controls and roam the network freely, using the PsExec Windows utility to remotely push ransomware to targeted systems.

According to a post on Twitter from Jan. 3, a research group called Bad Packets Report conducted a scan that revealed more than 3,800 Pulse VPN products that are still vulnerable to attacks.

Several government agencies across North America and the U.K. have already tried to urge organizations to address bugs in products such as Pulse VPNs, including the U.S. Cybersecurity and Infrastructure Security Agency (CISA) last October.

Don’t Make Your VPN a Risk Factor

VPNs are far from the only threat vector big game ransomware like REvil use to target their victims, of course. Other recent examples have included fake forums on compromised sites and malvertising campaigns.

Besides robust data backups, security experts say a good ransomware defense strategy should be based on security awareness training and anti-malware tools. In this case, however, simply making sure your organization is using the patch Pulse has already made available is the best course of action, perhaps coupled with a more detailed review of your patch management practices.