CVE-2026-55040 Details.
Microsoft SharePoint Server - JWT Authentication Bypass
Atlas does not check this one. Not a plain web check.
This weakness is not found through ordinary web pages. It needs a different kind of connection to the service. Atlas only runs plain web, DNS and TLS checks, so it does not run this one.
About CVE-2026-55040. What It Means.
Microsoft SharePoint Server is vulnerable to an authentication bypass (CVE-2026-55040) in its JWT token validation pipeline (SPJsonWebSecurityTokenHandlerV2). The chain disables signature requirements (RequireSignedTokens=false, accepting alg:none tokens), resolves the actor token x5t thumbprint against the server's own STS signing certificate (freely retrievable from /_layouts/15/metadata/json/1) without verifying the signature, accepts unregistered certificate issuers, and…
Affected Product. What Is Hit.
The record for CVE-2026-55040 does not name a vendor or product yet.
References. Where To Read More.
- https://github.com/sfewer-r7/CVE-2026-55040
- https://www.rapid7.com/blog/post/ra-microsoft-sharepoint-jwt-token-authentication-bypass-cve-2026-55040/
- https://nvd.nist.gov/vuln/detail/CVE-2026-55040
- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55040
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-55040
FAQ
Common Questions.
Microsoft SharePoint Server - JWT Authentication Bypass. Microsoft SharePoint Server is vulnerable to an authentication bypass (CVE-2026-55040) in its JWT token validation pipeline (SPJsonWebSecurityTokenHandlerV2). The chain disables signature requirements (RequireSignedTokens=false, accepting alg:none tokens), resolves the actor token x5t thumbprint against the server's own STS signing certificate (freely retrievable from /_layouts/15/metadata/json/1) without verifying the signature, accepts unregistered certificate issuers, and…
No. This weakness is not found through ordinary web pages. It needs a different kind of connection to the service. Atlas only runs plain web, DNS and TLS checks, so it does not run this one. The facts about CVE-2026-55040 are on this page, and you can request a demo to see how Brandefense watches your whole external attack surface.
Yes. CVE-2026-55040 is on the CISA Known Exploited Vulnerabilities list, which means attackers have used it against real targets.
Update the affected software to the latest version from the vendor, or follow the vendor's advice to switch off the affected feature. Vendor links are listed on this page when they are known.
This page lists the public facts about CVE-2026-55040. Atlas does not run a check for it, so nothing here says whether a particular site is affected.