CVE-2026-55040
Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.
Exploited in the wild
This vulnerability is on the CISA Known Exploited Vulnerabilities list, added 2026-08-18. Federal due date: 2026-08-21.
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.
Impact
Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.
Affected products
| Vendor | Product | Affected versions |
|---|---|---|
| Microsoft | Microsoft SharePoint Enterprise Server 2016 | from 16.0.0 before 16.0.5561.1001 |
| Microsoft | Microsoft SharePoint Server Subscription Edition | from 16.0.0 before 16.0.19725.20434 |
| Microsoft | Microsoft SharePoint Server 2019 | from 16.0.0 before 16.0.10417.20175 |
| Microsoft | Sharepoint Server | before 16.0.19725.20434 Versions 2016, 2019 |
Weakness classification
References
- NVD record
- CVE.org record
- GitHub advisory
- CISA KEV catalog
- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55040
- https://github.com/sfewer-r7/CVE-2026-55040
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-55040
- https://www.rapid7.com/blog/post/ra-microsoft-sharepoint-jwt-token-authentication-bypass-cve-2026-55040/