Security researchers say Microsoft customers should take immediate action to defend against the ongoing cyberattacks, and must assume they have already been compromised.

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.

Microsoft also has issued a patch for a related SharePoint vulnerability — CVE-2025-53771; Microsoft says there are no signs of active attacks on CVE-2025-53771, and that the patch is to provide more robust protections than the update for CVE-2025-49706.