What is CVE-2026-55040?
Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.
Timeline
- 2026-07-14Published to the U.S. National Vulnerability Database (NVD)
- 2026-08-12First covered in a defend.network daily briefing
- 2026-08-18Added to the CISA Known Exploited Vulnerabilities (KEV) catalog
- 2026-08-19NVD record last updated
- 2026-08-21CISA federal remediation deadline (BOD 22-01)
CISA Known Exploited Vulnerability
Microsoft SharePoint Weak Authentication Vulnerability
Affected product
Microsoft SharePoint
Remediation Steps
- Apply the vendor security update for Microsoft Sharepoint Server as a priority.
- Restrict network exposure of the affected service to trusted sources until patched.
- Review logs and detections for indicators of exploitation.
- Confirm fixed versions against the official vendor advisory before deploying.
References
- 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://nvd.nist.gov/vuln/detail/CVE-2026-55040
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog
Referenced in our briefings & reports
- Vulnerability Priority Report – Week 2 of September 2026 (September 14 – 20)
- Vulnerability Priority Report – Week 1 of September 2026 (September 7 – 13)
- Vulnerability Priority Report – Week 5 of August 2026 (August 31 – September 6)
- Vulnerability Priority Report – Week 4 of August 2026 (August 24 – 30)
- Vulnerability Priority Report – Week 3 of August 2026 (August 17 – 23)
- Vulnerability Priority Report – Week 2 of August 2026 (August 10 – 16)
- Microsoft, VMware, Apple vulnerabilities actively exploited; CISA KEV additions demand immediate patching (2026-08-20)
- SharePoint, Windows zero-day exploited; Lazarus backdoor in defense sector (2026-08-17)
- Microsoft patches 398 flaws; SharePoint exploited; Lazarus deploys Windows backdoor (2026-08-16)
- SharePoint, SAP, macOS flaws under active exploitation; 737 malicious Chrome extensions (2026-08-15)
- SharePoint auth bypass exploited; 737 Chrome VPN extensions abused; Microsoft patches 398 flaws (2026-08-14)
- Windows kernel zero-day exploited; Zoom annotation RCE, Sandworm VPN campaign (2026-08-12)
Browse all tracked CVEs in the defend.network CVE database →
🤖 This CVE page is generated by defend.network from NVD, CISA KEV, EPSS, and our verified daily briefings. Severity and exploitation data come from official sources; always verify remediation steps against the official vendor advisory before acting in production.