Reference page — cumulative record through Sunday, October 4, 2026 UTC. Reference pages update as the archive grows; only dated daily editions are immutable pages of record.

CVE-2026-55040

CVE-2026-55040CRITICAL

Microsoft SharePoint Server Security Feature Bypass Vulnerability

  AV  AC  PR  UI  S  C  I  A   CVSS    EPSS   %ile   KEV
   N   L   N   N  U  H  H  N    9.1   .1754   97.1   YES

AFFECTED
  Product                                           Versions  Fixed
  Microsoft SharePoint Enterprise Server 2016       16.0.0 –  —
  Microsoft SharePoint Server 2019                  16.0.0 –  —
  Microsoft SharePoint Server Subscription Edition  16.0.0 –  —

TIMELINE
  Jun 16  Reserved by microsoft
  Jul 14  Published (CNA: microsoft)
  Aug 18  ADDED TO KEV — CVE-2026-55040 (Microsoft SharePoint Enterprise Server 2016). Remediation due August 21, 2026.
  Aug 22  DUE DATE PASSED — CVE-2026-55040 (Microsoft SharePoint Enterprise Server 2016). CISA remediation deadline was August 21, 2026; still in catalog.

CWE-1390 · CNA: microsoft · CVSS v3.1 · 4 references · NVD status: Analyzed · KEV due August 21, 2026

Description

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

Lifecycle

Complete event history — 4 events, chronological
Date	Event	Detail
June 16, 2026	Reserved	Reserved by microsoft
July 14, 2026	Published	Published (CNA: microsoft)
August 18, 2026	KEV ADDED	ADDED TO KEV — CVE-2026-55040 (Microsoft SharePoint Enterprise Server 2016). Remediation due August 21, 2026.
August 22, 2026	DUE DATE PASSED	DUE DATE PASSED — CVE-2026-55040 (Microsoft SharePoint Enterprise Server 2016). CISA remediation deadline was August 21, 2026; still in catalog.

Affected

Affected products and packages — 3 rows
Vendor	Product / Package	Ecosystem	Version introduced	Fixed
Microsoft	Microsoft SharePoint Enterprise Server 2016	—	16.0.0	—
Microsoft	Microsoft SharePoint Server 2019	—	16.0.0	—
Microsoft	Microsoft SharePoint Server Subscription Edition	—	16.0.0	—

Weaknesses

CWE-1390

References (4)

https://github.com/sfewer-r7/CVE-2026-55040 [exploit]
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55040 [vendor-advisory, patch]
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-55040 [government-resource]
https://www.rapid7.com/blog/post/ra-microsoft-sharepoint-jwt-token-authentication-bypass-cve-2026-55040/ [technical-description]

Authoritative record: CVE-2026-55040 at cve.org

Vendors: microsoft

Weaknesses: CWE-1390

About this page

This is a reference page, not a dated page of record. It assembles the complete lifecycle of CVE-2026-55040 from the CVE Program record, NVD enrichment, the CISA KEV catalog, EPSS, and OSV advisories. The box score's numbers (CVSS, EPSS, KEV status) are current as of Sunday, October 4, 2026 UTC and are re-derived as the archive grows; only dated daily editions are immutable pages of record. The authoritative source for this identifier is cve.org.