Microsoft Issues Emergency .NET 10.0.7 Update to Patch Elevation of Privilege Vulnerability

Microsoft has issued an emergency out-of-band security update to address a severe vulnerability within the .NET framework.

The critical release of .NET 10.0.7 patches an Elevation of Privilege flaw that inadvertently surfaced after a recent routine system update.

Out-of-band patches bypass normal release schedules and indicate a pressing threat, meaning organizations relying on ASP.NET Core Data Protection must take immediate action to secure their infrastructure.

Uncovering CVE-2026-40372

The vulnerability, officially tracked as CVE-2026-40372, originated from a software regression introduced during the .NET 10.0.6 Patch Tuesday rollout.

Shortly after that release, software engineers began reporting unexpected decryption failures across various applications.

While investigating these decryption errors on GitHub, Microsoft security researchers uncovered that the underlying bug was not just a functional glitch, but a severe security loophole.

The root cause of the flaw lies with Microsoft.AspNetCore.DataProtection NuGet package. In the affected builds, the managed authenticated encryptor failed to process its Hash-based Message Authentication Code (HMAC) correctly.

The encryptor calculated the validation tag using the wrong payload bytes and then discarded the resulting hash.

This cryptographic failure compromises data integrity, potentially allowing an attacker to manipulate payloads and elevate their system privileges without triggering authentication alarms.

This vulnerability directly threatens any application that uses ASP.NET Core Data Protection to secure sensitive data. Security teams should audit their environments immediately to identify exposed assets.

• The flaw impacts Microsoft.AspNetCore.DataProtection package versions 10.0.0 through 10.0.6.
• Any .NET 10 deployments running the vulnerable runtime are highly susceptible to exploitation.
• Applications deployed in containers using unpatched .NET base images remain at risk until they are updated.

Immediate Remediation Steps

Fixing this vulnerability requires more than simply installing a system update on a server.

Development teams must manually update their project dependencies and redeploy their software to ensure complete protection against potential privilege escalation attacks.

• Download the latest .NET 10.0.7 SDK or Runtime directly from Microsoft’s official download portal.
• Confirm the update was successful by running the command dotnet –info in your terminal to verify the version number.
• Manually update the Microsoft.AspNetCore.DataProtection dependency on version 10.0.7 within your project configuration files.
• Rebuild your applications completely to bind the newly secured cryptographic libraries to your software.
• Redeploy the updated applications to your production environments using fresh container images or installation packages.

Developers encountering stability issues or unexpected behaviors during the patching process are encouraged to report anomalies through the .NET release feedback repository.

Maintaining active communication with Microsoft’s engineering team will help ensure the stability of future cryptographic updates.

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