CVE-2026-47300 Overview
CVE-2026-47300 is an elevation of privilege vulnerability in ASP.NET Core caused by an incorrect implementation of an authentication algorithm [CWE-303]. An authorized attacker on the network can abuse the flawed authentication logic to gain higher privileges than intended. The vulnerability affects confidentiality, integrity, and availability, and requires only low-level authenticated access with no user interaction.
Critical Impact
An authenticated network attacker can elevate privileges within ASP.NET Core applications, potentially gaining administrative access to resources and data protected by the affected authentication flow.
Affected Products
- ASP.NET Core (specific versions listed in the Microsoft Security Update CVE-2026-47300)
- Applications built on affected ASP.NET Core runtime versions
- Web services and APIs relying on the affected authentication component
Discovery Timeline
- 2026-07-14 - CVE-2026-47300 published to NVD
- 2026-07-15 - Last updated in NVD database
Technical Details for CVE-2026-47300
Vulnerability Analysis
CVE-2026-47300 stems from an incorrect implementation of an authentication algorithm within ASP.NET Core. The flaw is classified under [CWE-303], which covers incorrect implementation of authentication algorithms. When the authentication routine executes, it does not enforce the algorithm's intended checks correctly, allowing an authenticated caller to obtain privileges beyond their assigned role.
Because the attack vector is network-based and requires only low privileges without user interaction, the vulnerability is well suited for lateral movement following an initial foothold. Successful exploitation compromises confidentiality, integrity, and availability of the affected application and the resources it controls.
Root Cause
The root cause is a logic defect in how the authentication algorithm validates identity or session state. The implementation fails to verify a security-relevant condition before granting elevated privileges. Attackers who already hold a valid low-privilege identity can craft requests that exercise the flawed code path and receive access reserved for higher-privilege principals.
Attack Vector
An attacker first obtains legitimate authenticated access to the target ASP.NET Core application. From that authenticated session, the attacker issues requests that trigger the flawed authentication routine over the network. The application incorrectly treats the request as coming from a privileged principal and authorizes actions the attacker should not perform. No user interaction is required, and the attack complexity is low.
No public proof-of-concept code has been published. See the Microsoft Security Update CVE-2026-47300 advisory for vendor-supplied technical details.
Detection Methods for CVE-2026-47300
Indicators of Compromise
- Authenticated users performing actions or accessing resources outside their assigned role scope.
- Unexpected role or claim changes in authentication tokens issued by the ASP.NET Core application.
- Sudden increases in successful authorization decisions for sensitive endpoints from low-privilege accounts.
Detection Strategies
- Audit ASP.NET Core authentication and authorization logs for principals accessing resources beyond their normal role boundaries.
- Correlate authenticated session identifiers with the endpoints accessed to identify privilege boundary violations.
- Compare issued token claims against expected role assignments in the identity provider.
Monitoring Recommendations
- Enable verbose authentication logging in ASP.NET Core middleware and forward events to a centralized SIEM.
- Monitor administrative endpoints for calls from accounts that historically never touched them.
- Alert on authentication algorithm exceptions, fallback paths, and anomalous claim transformations.
How to Mitigate CVE-2026-47300
Immediate Actions Required
- Apply the updates referenced in the Microsoft Security Update CVE-2026-47300 advisory to all affected ASP.NET Core runtimes and applications.
- Inventory internally developed and third-party applications that depend on the affected ASP.NET Core versions.
- Rotate authentication secrets, signing keys, and long-lived tokens issued by affected applications after patching.
Patch Information
Microsoft has published guidance and update packages for CVE-2026-47300. Refer to the Microsoft Security Update CVE-2026-47300 entry for affected version ranges, fixed builds, and deployment instructions. Rebuild and redeploy self-contained ASP.NET Core applications against the patched runtime.
Workarounds
- Restrict network exposure of affected ASP.NET Core applications to trusted networks until patching is complete.
- Enforce least-privilege role assignments so that a successful elevation yields the smallest possible privilege gain.
- Add compensating authorization checks at the controller or middleware layer to re-validate principal claims for sensitive actions.
Refer to the Microsoft Security Update CVE-2026-47300 advisory for vendor-recommended configuration guidance.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
