SharePoint: critical auth bypass by Rapid7

Today sees the publication of CVE-2026-55040, a critical authentication bypass in Microsoft SharePoint. Discovered by Rapid7 Senior Principal Security Researcher Stephen Fewer, and published today in coordination with Microsoft, this vulnerability is the first in a pair of exploits which, when chained together, can lead to unauthenticated remote code execution against a vulnerable SharePoint server. Patches are available for SharePoint Server Subscription Edition, 2019, and 2016. As the full Rapid7 blog post sets out, the second vulnerability in the full RCE chain remains embargoed for now, with Microsoft expected to publish patches for that second vulnerability as part of Patch Tuesday August 2026. Microsoft noted: “We would like to thank Rapid7 for responsibly reporting this issue through coordinated vulnerability disclosure.