Published Tuesday, July 14, 2026 at 07:41 AM PT

<strong>MICROSOFT SHAREPOINT ZERO-DAY: AUTHENTICATION BYPASS DISCLOSED (CVE-2026-55040)</strong>

BLUF: Rapid7 Labs and Microsoft jointly disclosed CVE-2026-55040, an unauthenticated authentication bypass in Microsoft SharePoint. This vulnerability is the first component of a chained exploit that achieves remote code execution when combined with a second, yet-to-be-patched vulnerability. Organizations running vulnerable SharePoint instances should prioritize immediate assessment and prepare for patching upon Microsoft’s release.

DETAILS:

  • Rapid7 Labs conducted zero-day research resulting in discovery of two chained vulnerabilities affecting Microsoft SharePoint
  • CVE-2026-55040 (authentication bypass) is disclosed today; the RCE component remains under embargo pending Microsoft patch release
  • The exploit chain achieves unauthenticated remote code execution against vulnerable SharePoint servers
  • UNCERTAIN: Specific patch timeline from Microsoft not provided in available disclosure materials
  • UNCERTAIN: Affected SharePoint versions and configurations not yet detailed in public advisory

IMPACT:

  • Scope: Organizations operating Microsoft SharePoint infrastructure
  • Risk Level: CRITICAL — unauthenticated RCE capability represents maximum severity
  • Affected Systems: SharePoint deployments matching vulnerability criteria (version/configuration details pending full advisory)
  • Exposure: Internet-facing or network-accessible SharePoint instances are immediately at risk once exploit details circulate

RECOMMENDED ACTIONS:

  1. IMMEDIATE: Identify and inventory all SharePoint deployments in your environment
  2. IMMEDIATE: Restrict network access to SharePoint servers where operationally feasible pending patch availability
  3. URGENT: Monitor Microsoft Security Response Center (MSRC) for CVE-2026-55040 advisory with affected versions and patch timeline
  4. URGENT: Prepare change management and testing procedures for emergency patching
  5. ONGOING: Monitor for any public exploit code or active exploitation attempts

SOURCES:

  • Rapid7 Labs disclosure (joint with Microsoft)
  • Microsoft security advisory (pending full MSRC publication)