Security researchers at Google and Microsoft say they have evidence that hackers backed by China are exploiting a zero-day bug in Microsoft SharePoint, as companies around the world scramble to patch the flaw.

The bug, known officially as CVE-2025-53770 and discovered last weekend, allows hackers to steal sensitive private keys from self-hosted versions of SharePoint, a software server widely used by companies and organizations to store and share internal documents. Once exploited, an attacker can use the bug to remotely plant malware and gain access to the files and data stored within, as well as gain access to other systems on the same network.