CVE-2026-40372

Improper verification of cryptographic signature in ASP.NET Core allows an unauthorized attacker to elevate privileges over a network.

Improper verification of cryptographic signature in ASP.NET Core allows an unauthorized attacker to elevate privileges over a network.

Executive Summary:

A bug in Microsoft.AspNetCore.DataProtection 10.0.0-10.0.6 NuGet packages can give an attacker the opportunity to execute an Elevation of Privilege attack by forging authentication cookies, and also allows some protected payloads to be decrypted.

If an attacker used forged payloads to authenticate as a privileged user during the vulnerable window, they may have induced the application to issue legitimately-signed tokens (session refresh, API key, password reset link, etc.) to themselves. Those tokens remain valid after upgrading to 10.0.7 unless the DataProtection key ring is rotated.

This is comparable in capability to MS10-070, which exploited a similar padding-oracle condition in ASP.NET's legacy encryption infrastructure.

Announcement

Announcement for this issue can be found at https://github.com/dotnet/announcements/issues/395

CVSS Details

• Version: 3.1
• Severity: Important
• Score: 9.1
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
• Weakness: CWE-347: Improper Verification of Cryptographic Signature

Affected Platforms

• Platforms: All
• Architectures: All

<a name="affected-packages"></a>Affected Packages

The vulnerability affects some Microsoft .NET projects if they use any of affected package versions listed below

<a name="ASP.NET Core 10"></a>ASP.NET Core 10

Package name | Affected version | Patched version ------------ | ---------------- | ------------------------- Microsoft.AspNetCore.DataProtection | >=10.0.0, <=10.0.6 | 10.0.7

Advisory FAQ

<a name="how-affected"></a>How do I know if I am affected?

Primary affected configuration (10.0.6 on net10.0)

You are affected if ALL of the following are true:

• Your application referenced Microsoft.AspNetCore.DataProtection version 10.0.6 from NuGet (directly or transitively via, e.g., Microsoft.AspNetCore.DataProtection.StackExchangeRedis, .EntityFrameworkCore, .AzureKeyVault, .AzureStorage, .Redis), AND The affected 10.0.6 NuGet binary was actually loaded at runtime. This happens when either the application does NOT target the Microsoft.NET.Sdk.Web NOR has a Microsoft.AspNetCore.App framework reference either directly or transitively UNLESS you opt out of PrunePackageReference which is enabled by default in .NET 10.
• The application ran on Linux, macOS, or any non-Windows operating system.

Secondary affected configuration (10.0.x on net462 / netstandard2.0)

You are also affected if:

• Your application or library referenced Microsoft.AspNetCore.DataProtection versions 10.0.0 through 10.0.6 from NuGet, AND
• The build consumed the net462 or netstandard2.0 target framework asset of that package. This occurs when your application does not target net10.0 and consumes the package (e.g. net8.0, net9.0, net481 for mono, etc.). This combination is unusual because 10.0 NuGet packages are generally intended for use with .NET 10.

This secondary population is much smaller and is expected to primarily consist of:

• Desktop or server applications on .NET Framework that happen to use the ASP.NET Core DataProtection NuGet package.
• Libraries that target netstandard2.0 and reference the 10.0 DataProtection package.

These configurations use the same managed authenticated encryptor code path on all operating systems (the CNG path is only available on the net10.0 asset), so the Windows exception below does not apply to them.

Not affected

• Your application runs on Windows
• Your application runs framework-dependent on net10.0 and your installed ASP.NET Core shared framework version is ≥ your PackageReference version of Microsoft.AspNetCore.DataProtection. In this case the (correct) shared framework copy is loaded and the NuGet copy…

Improper verification of cryptographic signature in ASP.NET Core allows an unauthorized attacker to elevate privileges over a network.

Improper verification of cryptographic signature in ASP.NET Core allows an unauthorized attacker to elevate privileges over a network.

Improper verification of cryptographic signature in ASP.NET Core allows an unauthorized attacker to elevate privileges over a network.