Microsoft Corp. has confirmed that its SharePoint server software is under active attack by unidentified hackers, prompting concerns over a widespread cybersecurity threat.

The company said it has issued a security patch to help customers protect their on-premises servers, adding that more fixes are being developed.

The US Cybersecurity and Infrastructure Security Agency also acknowledged the vulnerability, noting that it could allow attackers to access internal systems, manipulate file configurations, and execute malicious code remotely.

Cybersecurity experts warned that thousands of organizations worldwide could be exposed.

Silas Cutler, a researcher at Michigan-based Censys, estimated that over 10,000 companies using SharePoint servers are at risk—most of them in the United States, followed by the Netherlands, United Kingdom, and Canada.

“It’s a dream for ransomware operators, and a lot of attackers are going to be working this weekend as well,” he added.

Palo Alto Networks Inc. warned that “these exploits are real, in-the-wild, and pose a serious threat.”

Google’s Threat Intelligence Group confirmed in an emailed statement that it had observed hackers actively exploiting the SharePoint vulnerability.

The group warned that the flaw enables “persistent, unauthenticated access” and poses a serious threat to affected organizations.

According to The Washington Post, the breach has impacted U.S. federal and state agencies, universities, energy firms, and even an Asian telecommunications company, citing information from state officials and private cybersecurity researchers.

This incident adds to a string of recent cyberattacks targeting Microsoft.

In March, the company warned that Chinese hackers were exploiting remote management tools and cloud applications to conduct espionage against organizations both in the U.S. and internationally.