Sophos said it is fixing a vulnerability in its Cyberoam firewall appliances, which a security researcher says can allow an attacker to gain access to a company’s internal network without needing a password.

The vulnerability allows an attacker to remotely gain “root” permissions on a vulnerable device, giving them the highest level of access, by sending malicious commands across the internet. The attack takes advantage of the web-based operating system that sits on top of the Cyberoam firewall.

Once a vulnerable device is accessed, an attacker can jump onto a company’s network, according to the researcher who shared their findings exclusively with TechCrunch.

Cyberoam devices are typically used in large enterprises, sitting on the edge of a network and acting as a gateway to allow employees in while keeping hackers out. These devices filter out bad traffic, and prevent denial-of-service attacks and other network-based attacks. They also include virtual private networking (VPN), allowing remote employees to log on to their company’s network when they are not in the office.

It’s a similar vulnerability to recently disclosed flaws in corporate VPN providers, notably Palo Alto Networks, Pulse Secure and Fortinet, which allowed attackers to gain access to a corporate network without needing a user’s password. Many large tech companies, including Twitter and Uber, were affected by the vulnerable technology, prompting Homeland Security to issue an advisory to warn of the risks.

Sophos, which bought Cyberoam in 2014, issued a short advisory this week, noting that the company rolled out fixes on September 30.

The researcher, who asked to remain anonymous, said an attacker would only need an IP address of a vulnerable device. Getting vulnerable devices was easy, they said, by using search engines like Shodan, which lists around 96,000 devices accessible to the internet. Other search engines put the figure far higher.

A Sophos spokesperson disputed the number of devices affected, but would not provide a clearer figure.

“Sophos issued an automatic hotfix to all supported versions in September, and we know that 99% of devices have already been automatically patched,” said the spokesperson. “There are a small amount of devices that have not as of yet been patched because the customer has turned off auto-update and/or are not internet-facing devices.”

Customers still affected can update their devices manually, the spokesperson said. Sophos said the fix will be included in the next update of its CyberoamOS operating system, but the spokesperson did not say when that software would be released.

The researcher said they expect to release the proof-of-concept code in the coming months.