CVE-2026-55040

Microsoft SharePoint Server Security Feature Bypass Vulnerability

Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.

Affected

Microsoft · Microsoft SharePoint Enterprise Server 2016 · Microsoft SharePoint Server 2019 · Microsoft SharePoint Server Subscription Edition

CVSS v3.1 MICROSOFT

9.1 CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

EPSS

69.54% chance of exploitation in the next 30 days, 99th percentile

CISA KEV

added 2026-08-18

Nuclei

critical · CWE-1390

Published

2026-07-14

Updated

2026-10-08

Proof-of-concept exploits (5)

• l0ggg/CVE-2026-550403★ · 2026-07-28
• sfewer-r7/CVE-2026-5504059★ · 2026-08-10
• hypnguyen1209/CVE-2026-635201★ · 2026-08-26
• zenzue/CVE-2026-550400★ · 2026-08-26
• maxprog-svg/CVE-2026-55040-Mass-Exploit0★ · 2026-08-27

Nuclei templates (1)

• projectdiscovery/nuclei-templates/blob/main/javascript/cves/2026/CVE-2026-55040.yaml

Security advisories

• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55040
• https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-55040

References

• CVE Record
• NVD entry

Related

• CVE-2023-27532
• CVE-2023-34362
• CVE-2024-51977
• CVE-2024-51978
• CVE-2024-51979
• CVE-2024-51980