CVE-2026-55040
Critical 9.1 Exploited in the wild (KEV)
Confirmed active exploitation — CISA KEV catalog
- Name
- Microsoft SharePoint Weak Authentication Vulnerability
- Added to catalog
- Remediation due date (US federal)
- Required action
- Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.
Description
Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.
Metrics
- CVSS 3.1
-
9.1 (CRITICAL)
Score source: CNA
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N - EPSS — exploit probability
- 70% (percentile: 99) as of 1 November 2026
- CWE
- CWE-1390
Affected products
microsoft: sharepoint server
References
- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55040 PatchVendor Advisory
- https://github.com/sfewer-r7/CVE-2026-55040 Exploit
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026… ExploitThird Party Advisory
- https://www.rapid7.com/blog/post/ra-microsoft-sharepoint-jwt-token-authenticati… US Government Resource