🔥 This vulnerability is being actively exploited in the wild (CISA Known Exploited Vulnerabilities catalog)
CVE-2026-55040: Microsoft SharePoint Weak Authentication Vulnerability
Summary
Microsoft SharePoint has a weak authentication vulnerability that allows attackers to bypass security features over a network without proper credentials. This flaw is currently being exploited by real attackers. Organizations must apply patches according to Microsoft's instructions and follow CISA's BOD 26-04 guidance (a federal directive for prioritizing security updates), or stop using the product if no fix is available.
Solution / Mitigation
Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA's BOD 26-04 guidance. For cloud services, follow applicable BOD 26-04 guidance or discontinue use of the product if mitigations are unavailable. See Microsoft Security Response Center (https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55040) for specific patches. Due date for patching: 2026-08-21.
Vulnerability Details
EPSS: 4.0%
Yes
🔥 Actively Exploited
August 17, 2026
Classification
Taxonomy References
Affected Vendors
Related Issues
Original source: https://nvd.nist.gov/vuln/detail/CVE-2026-55040
First tracked: August 18, 2026 at 02:01 PM
Classified by LLM (prompt v3) · confidence: 72%