Microsoft is issuing an emergency fix to close off a vulnerability in Microsoft’s SharePoint software that hackers have exploited to carry out widespread attacks on businesses and at least some federal agencies.

A cyber-espionage campaign centered on vulnerable versions of Microsoft's server software now involves the deployment of ransomware, Microsoft said in a late Wednesday blog post.

A China-linked threat actor has been observed exploiting SharePoint servers to deliver ransomware, according to Microsoft researchers, in the latest sign of worsening attacks against on-premises SharePoint Server customers.