NEW YORK (AP) — Microsoft has issued an emergency fix to close off a vulnerability in Microsoft's widely-used SharePoint software that hackers have exploited to carry out widespread attacks on businesses and at least some U.S. government agencies.
The company issued an alert to customers Saturday saying it was aware of the zero-day exploit being used to conduct attacks and that it was working to patch the issue. Microsoft updated its guidance Sunday with instructions to fix the problem for SharePoint Server 2019 and SharePoint Server Subscription Edition. Engineers were still working on a fix for the older SharePoint Server 2016 software.
"Anybody who's got a hosted SharePoint server has got a problem," said Adam Meyers, senior vice president with CrowdStrike, a cybersecurity firm. "It's a significant vulnerability."
Companies and government agencies around the world use SharePoint for internal document management, data organization and collaboration.
What is a zero-day exploit?
A zero-day exploit is a cyberattack that takes advantage of a previously unknown security vulnerability. "Zero-day" refers to the fact that the security engineers have had zero days to develop a fix for the vulnerability.
According to the U.S. Cybersecurity and Infrastructure Security Agency (CISA), the exploit affecting SharePoint is "a variant of the existing vulnerability CVE-2025-49706 and poses a risk to organizations with on-premise SharePoint servers."
Security researchers warn that the exploit, reportedly known as "ToolShell," is a serious one and can allow actors to fully access SharePoint file systems, including services connected to SharePoint, such as Teams and OneDrive.
Google's Threat Intelligence Group warned that the vulnerability may allow bad actors to "bypass future patching."
How widespread is the impact?
Eye Security said in its blog post that it scanned over 8,000 SharePoint servers worldwide and discovered that at least dozens of systems were compromised. The cybersecurity company said the attacks likely began on July 18.
The vulnerability potentially affects government agencies, schools, healthcare systems and companies.
Microsoft said the vulnerability affects only on-site SharePoint servers used within businesses or organizations, and does not affect Microsoft's cloud-based SharePoint Online service.
What do you do now?
The vulnerability targets SharePoint server software so customers of that product will want to immediately follow Microsoft's guidance to patch their systems.
Although the scope of the attack is still being assessed, CISA warned that the impact could be widespread and recommended that any servers impacted by the exploit should be disconnected from the internet until they are patched. Microsoft engineers also recommend pulling affected systems offline until fixes can be applied.
