CVE-2026-55040
Microsoft SharePoint Server Security Feature Bypass Vulnerability
- Published
- Jul 14, 2026
- Updated
- Sep 17, 2026
- Assigning CNA
- microsoft
- Evidence observed
- Aug 18, 2026
Primary CVSS
nvd · CVSS 3.1
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:NHigh · next 30 days
- Percentile
- 98.9%
- Model date
- Sep 21, 2026
EPSS is a statistical estimate, not a certainty or a measure of impact. Combine it with CVSS, KEV status, exposure and your environment.
CISA Known Exploited
This CVE appears in the CISA Known Exploited Vulnerabilities catalog.
Summary
Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.
Sources
5- CVE-2026-63520Exploit
Exploit chain for unauthenticated RCE on Microsoft SharePoint, combining a JWT authentication bypass with unsafe .NET type instantiation to achieve code execution as the service account.
- CVE-2026-55040-Mass-ExploitExploit
Exploit for CVE-2026-55040 in Microsoft SharePoint, forging JWT tokens via algorithm none, weak HS256 secrets, and RS256 substitution to impersonate users, including mass attack mode.
- CVE-2026-55040Exploit
Proof-of-concept exploit for Microsoft SharePoint CVE-2026-55040 that forges JWT tokens, bypasses authentication, auto-discovers metadata, and impersonates site admins via SID enumeration.
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