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.

Threat actors exploit SharePoint flaws to access internal systems, steal sensitive data, and carry out surveillance, impersonation, and extortion.

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.