CVE-2026-55040
Microsoft SharePoint Server Security Feature Bypass Vulnerability
Microsoft SharePoint Weak Authentication Vulnerability is confirmed as actively exploited and is listed in the CISA KEV catalog.
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.
CISA notes
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55040 ; BOD 26-04: https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk ; Forensics Triage Requirements: https://www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk ; https://nvd.nist.gov/vuln/detail/CVE-2026-55040
Description
Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.
Severity
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N/E:U/RL:O/RC:CExploitation Context
as of October 15, 2026- CISA added CVE-2026-55040 to the KEV catalog 35 days after its CVE record was published. The median for entries added in 2026 so far is 14 days.
- It is one of 391 Microsoft entries in the CISA KEV catalog, and one of 40 added in 2026.
- Its current EPSS score (69.5%) is higher than that of 58% of CISA KEV entries.
Affected Products
| Vendor | Product | Affected versions |
|---|---|---|
| Microsoft | Microsoft Microsoft SharePoint Enterprise Server 2016 | 16.0.0 to <16.0.5561.1001 |
| Microsoft | Microsoft Microsoft SharePoint Server 2019 | 16.0.0 to <16.0.10417.20175 |
| Microsoft | Microsoft Microsoft SharePoint Server Subscription Edition | 16.0.0 to <16.0.19725.20434 |
References
1 LinksRecord Details
More from Microsoft
Microsoft SharePoint Server Remote Code Execution Vulnerability
Microsoft SharePoint Remote Code Execution Vulnerability
Microsoft SharePoint Remote Code Execution Vulnerability
Microsoft SharePoint Server Spoofing Vulnerability
Related
Tool categories
CVE record data © The MITRE Corporation, used under the CVE Terms of Use. Exploited-in-the-wild data from the CISA Known Exploited Vulnerabilities catalog (CC0). Exploit prediction scores by FIRST EPSS (first.org/epss). This site is not endorsed or certified by MITRE, NVD, CISA, or FIRST.