Microsoft Security Advisory 4010983

Vulnerability in ASP.NET Core MVC 1.1.0 Could Allow Denial of Service

Published: January 27, 2017

Version: 1.0


Executive Summary

Microsoft is releasing this security advisory to provide information about a vulnerability in the public versions of ASP.NET Core MVC 1.1.0. This advisory also provides guidance on what developers can do to update their applications correctly.

Microsoft is aware of a security vulnerability in the public version of ASP.NET Core MVC 1.1.0 where a malformed HTTP request could lead to a denial of service.

ASP.NET Core is next generation of ASP.NET that provides a familiar and modern framework for web and cloud scenarios, running on top of .NET Core. These products are actively developed by the ASP.NET team in collaboration with a community of open source developers, running on Windows, Mac OS X and Linux. When ASP.NET Core was released, the version number was reset to 1.0.0 to reflect the fact that it is a separate product from its predecessor - ASP.NET.

Developers are advised to update all apps to use package version 1.1.1 or greater.

Mitigating Factors

Only applications targeting ASP.NET Core 1.1.0 are affected. Applications targeting ASP.NET Core 1.0.0, 1.0.1 or 1.02 are not affected.

Affected Software

The vulnerability affects any Microsoft ASP.NET Core project if it uses the following affected package version.

Affected package and version

Package name

Package version

Microsoft.AspNetCore.Mvc.Core

1.1.0

Advisory FAQ

How do I know if I am affected? 
ASP.NET Core has two different types of dependencies, direct and transitive. If your project has a direct or transitive dependency on Microsoft.AspNetCore.Mvc.Core version 1.1.0 you are affected.

.NET Core Project formats

.NET Core has two different project file formats, depending on what software created the project.

  1. project.json is the original format, included in .NET Core 1.0 and Visual Studio 2015.
  2. csproj is the format used in Visual Studio 2017.

You must ensure you follow the correct update instructions for your project type.

Direct Dependencies

Direct dependencies are dependencies where you specifically add a package to your project. For example, if you add the Microsoft.AspNetCore.Mvc package to your project then you have taken a direct dependency on Microsoft.AspNetCore.Mvc.

Direct dependencies are discoverable by reviewing your project.json or csproj file.

Transitive Dependencies

Transitive dependencies occur when you add a package to your project that in turn relies on another package. For example, if you add the Microsoft.AspNetCore.Mvc package to your project it depends on the Microsoft.AspNetCore.Mvc.Core package (amongst others). Your project has a direct dependency on Microsoft.AspNetCore.Mvc and a transitive dependency on the Microsoft.AspNetCore.Mvc.Core package.

Transitive dependencies are reviewable in the Visual Studio Solution Explorer window, which supports searching, or by reviewing the project.lock.json file contained in the root directory of your project for project.json projects or the project.assets.json file contained in the obj directory of your project for csproj projects. These files are the authoritative list of all packages used by your project, containing both direct and transitive dependencies.

Any ASP.NET Core MVC 1.1 application will have a dependency on the affected package, either direct or transitive

How do I fix my affected app?

You will need to fix both direct dependencies and review and fix any transitive dependencies. Version 1.1.1 of the vulnerable package contains the fixes required to secure your app.

Fixing Direct Dependencies – project.json/VS2015

Open your project.json file in your editor. Look for the dependencies section. Below is an example dependencies section:

  "dependencies": {
    "Microsoft.NETCore.App": {
      "version": "1.1.0",
      "type": "platform"
    },
    "Microsoft.AspNetCore.Server.Kestrel": "1.1.0",
    "Microsoft.AspNetCore.Mvc.Core": "1.1.0",
  }

This example has three direct dependencies, Microsoft.NetCore.App, Microsoft.AspNetCore.Server.Kestrel and Microsoft.AspNetCore.Mvc.Core.

Microsoft.NetCore.App is the platform the application targets, you should ignore this. The other packages expose their version is to the right of the package name, in our example our non-platform packages are version 1.1.0.

Review your direct dependencies for any instance of Microsoft.AspNetCore.Mvc.Core version 1.1.0, in the example above there is a direct dependency on the vulnerable package.

To update to the new package, change the version number to be 1.1.1. After updating the vulnerable package version save your project.json file.

Mt778901.note(en-us,Security.10).gifNote:
As part of patching ASP.NET Core MVC we update every Microsoft.AspNetCore.Mvc.* package. If, for example, you have a dependency on Microsoft.AspNetCore.Mvc you should update its version to 1.1.1, and it will also update the vulnerable Microsoft.AspNetCore.Mvc.Core package.

The dependencies section in our example project.json would now look as follows:

  "dependencies": {
    "Microsoft.NETCore.App": {
      "version": "1.1.0",
      "type": "platform"
    },
    "Microsoft.AspNetCore.Server.Kestrel": "1.1.0",
    "Microsoft.AspNetCore.Mvc.Core": "1.1.1",
  }

If you are using Visual Studio and save your updated project.json file Visual Studio will restore the new package version. You can see the restore results by opening the Output Window (Ctrl+Alt+O) and change the “Show output from” drop down to Package Manager.

If you are not using Visual Studio open a command line and change to your project directory. Execute the dotnet restore command to restore your new dependency.

Once you have addressed all your direct dependencies you must also review your transitive dependencies.

Fixing Direct Dependencies – csproj/VS2017

Open your projectname.csproj file in your editor, or right click on the project in Visual Studio 2017 and choose Edit projectname.csproj from the content menu, where projectname is the name of your project. Look for PackageReference nodes. Below shows an example project file:

<Project ToolsVersion="15.0" Sdk="Microsoft.NET.Sdk.Web">
  <PropertyGroup>
    <TargetFramework>netcoreapp1.1</TargetFramework>
  </PropertyGroup>
  <PropertyGroup>
    <PackageTargetFallback>$(PackageTargetFallback);portable-net45+win8+wp8+wpa81;</PackageTargetFallback>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="Microsoft.AspNetCore" Version="1.1.0" />
    <PackageReference Include="Microsoft.AspNetCore.Mvc.Core" Version="1.1.0" />
  </ItemGroup>
  <ItemGroup>
    <DotNetCliToolReference Include="Microsoft.VisualStudio.Web.CodeGeneration.Tools" Version="1.0.0-msbuild3-final" />
  </ItemGroup>
</Project> 

The example has two direct package dependencies, as seen by the two PackageReference elements. The name of the package is in the Include attribute, and the package version number is in the Version attribute expose their version is to the right of the package name. The example shows two packages Microsoft.AspNetCore and Microsoft.AspNetCore.Mvc.Core and each package is version 1.1.0.

Review your PackageReference elements for any instance of Microsoft.AspNetCore.Mvc.Core version 1.1.0.

If a reference is present update to the new package by change the Version attribute value to be 1.1.1. After updating the vulnerable package version save your csproj file.

Mt778901.note(en-us,Security.10).gifNote:
As part of patching ASP.NET Core MVC we update every Microsoft.AspNetCore.Mvc.* package. If, for example, you have a dependency on Microsoft.AspNetCore.Mvc you should update its version to 1.1.1, and it will also update the vulnerable Microsoft.AspNetCore.Mvc.Core package.

The example csproj would now look as follows:

<Project ToolsVersion="15.0" Sdk="Microsoft.NET.Sdk.Web">
  <PropertyGroup>
    <TargetFramework>netcoreapp1.1</TargetFramework>
  </PropertyGroup>
  <PropertyGroup>
    <PackageTargetFallback>$(PackageTargetFallback);portable-net45+win8+wp8+wpa81;</PackageTargetFallback>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="Microsoft.AspNetCore" Version="1.1.0" />
    <PackageReference Include="Microsoft.AspNetCore.Mvc.Core" Version="1.1.1" />
  </ItemGroup>
  <ItemGroup>
    <DotNetCliToolReference Include="Microsoft.VisualStudio.Web.CodeGeneration.Tools" Version="1.0.0-msbuild3-final" />
  </ItemGroup>
</Project> 

If you are using Visual Studio and save your updated csproj file Visual Studio will restore the new package version. You can see the restore results by opening the Output Window (Ctrl+Alt+O) and change the “Show output from” drop down to Package Manager.

If you are not using Visual Studio open a command line and change to your project directory. Execute the dotnet restore command to restore your new dependency.

Once you have addressed all your direct dependencies you must also review your transitive dependencies.

Reviewing Transitive Dependencies

There are two ways to view transitive dependencies. You can use Visual Studio’s Solution Explorer, or by reviewing your project.lock.json (project.json/VS2015) or project.assets.json (csproj/VS2017) file.

Using Visual Studio Solution Explorer (VS2015)

If you want to use Visual Studio 2015 open your project in Visual Studio 2015 then press Ctrl+; to activate the search in Solution Explorer. Search for Microsoft.AspNetCore.Mvc.Core and make a note of the version numbers of any results you find.

For example, searching for Microsoft.AspNetCore.Mvc.Core in an example project that contains a reference to Microsoft.AspNetCore.Mvc shows the following results in Visual Studio 2015;

Mt778901.9827B9BDFB5B91DF15829FAFEB42854E(en-us,Security.10).png

Figure 1: Searching references in Visual Studio 2015

The search results appear as a tree. In these results, you can see we have found references to Microsoft.AspNetCore.Mvc.Core, version 1.1.0, the vulnerable version.

The first entry under the References heading refers to the target framework your application is using. This will be .NETCoreApp, .NETStandard or .NET-Framework-vX.Y.Z (where X.Y.Z is an actual version number) depending on how you configured your application. Underneath your target framework will be the list of packages you have directly taken a dependency on. In this example the application takes a dependency on Microsoft.AspNetCore.Mvc. Microsoft.AspNetCore.Mvc in turn has leaf nodes that list its dependencies and their versions. In this case the Microsoft.AspNetCore.Mvc package takes a dependency on a vulnerable version of Microsoft.AspNetCore.Mvc.Core and numerous other packages.

Manually reviewing project.lock.json (project.json/VS2015)

Open the project.lock.json file in your editor. We suggest you use an editor that understands json and allows you to collapse and expand nodes to review this file; both Visual Studio and Visual Studio Code provide this functionality.

If you are using Visual Studio the project.lock.json file is “underneath” the project.json file. Click the right pointing triangle, ▷, to the left of the project.json file to expand the solution tree to expose the project.lock.json file. Figure 1 below shows a project with the project.json file expanded to show the project.lock.json file.

Mt778901.10871F6DAB46208F3A20B4D79DC43612(en-us,Security.10).png

Figure 2: project.lock.json file location

Search the project.lock.json file for the string “Microsoft.AspNetCore.Mvc.Core/1.1.0”. If your project.lock.json file includes this string, you have a dependency on the vulnerable package.

Fixing transitive dependencies (project.json/VS2015)

If you have not found any reference to Microsoft.AspNetCore.Mvc.Core/1.1.0 this means none of your direct dependencies depend on the vulnerable version of Microsoft.AspNetCore.Mvc.Core or you have already fixed the problem by updating the direct dependencies.

If your transitive dependency review found references to the vulnerable Microsoft.AspNetCore.Mvc.Core/1.1.0 you must add a direct dependency to the updated package to your project.json file to override the transitive dependency. Open your project.json and find the dependencies section. For example:

  "dependencies": {
    "Microsoft.NETCore.App": {
      "version": "1.1.0",
      "type": "platform"
    },
    "Microsoft.AspNetCore.Server.Kestrel": "1.1.0",
    "Microsoft.AspNetCore.Mvc": "1.1.0"
  }

The results of our transitive package search showed us that Microsoft.AspNet.Mvc depends on Microsoft.AspNet.Mvc.Core version 1.1.0. To fix this you must add a direct dependency by adding it to the project.json file. You do this by adding a new line to the dependencies section, referring the fixed version. For example, to pull in the fixed version of Microsoft.AspNet.Mvc.Core, version 1.1.1 you edit the project.json file as follows;

  "dependencies": {
    "Microsoft.NETCore.App": {
      "version": "1.1.0",
      "type": "platform"
    },
    "Microsoft.AspNetCore.Mvc.Core": "1.1.1",
    "Microsoft.AspNetCore.Server.Kestrel": "1.1.0",
    "Microsoft.AspNetCore.Mvc.Core ": "1.1.0"
  }

Once you have added direct dependencies to the fixed packages save your project.json file.

If you are using Visual Studio save your updated project.json file and Visual Studio will restore the new package versions. You can see the restore results by opening the Output Window (Ctrl+Alt+O) and change the “Show output from” drop down to Package Manager.

If you are not using Visual Studio open a command line and change to your project directory. Execute the dotnet restore command to restore your new dependencies.

Using Visual Studio Solution Explorer (VS2017)

If you want to use Solution Explorer open your project in Visual Studio 2017, then press Ctrl+; to activate the search in Solution Explorer. Search for Microsoft.AspNetCore.Mvc.Core and make a note of the version numbers of any results you find.

For example, searching for Microsoft.AspNetCore.Mvc.Core in an example project that contains a package that takes a dependency on Microsoft.AspNetCore.Mvc shows the following results in Visual Studio 2017;

Mt778901.97811781D263F93FEA81D3888A3EC4D8(en-us,Security.10).png

Figure 3: Searching references in Visual Studio 2017

The search results appear as a tree. In these results, you can see we have found references to Microsoft.AspNetCore.Mvc.Core version 1.1.0.

Underneath the Dependencies node will be a NuGet node. Under the NuGet node will be the list of packages you have directly taken a dependency on and their versions. In this example the application takes a direct dependency on Microsoft.AspNetCore.Mvc. Microsoft.AspNetCore.Mvc in turn has leaf nodes that list its dependencies and their versions. In the example the Microsoft.AspNetCore.Mvc package takes a dependency on a version of Microsoft.AspNetCore.Mvc.ApiExplorer which in turn takes a dependency on a vulnerable version of Microsoft.AspNetCore.Mvc.Core. You can see that other packages also take a dependency on the vulnerable version of Microsoft.AspNetCore.Mvc.Core.

Manually reviewing project.assets.json (VS2017)

Open the project.assets.json file from your project’s obj directory in your editor. We suggest you use an editor that understands json and allows you to collapse and expand nodes to review this file; both Visual Studio and Visual Studio Code provide this functionality.

Search the project.assets.json file for the string “Microsoft.AspNetCore.Mvc.Core/1.1.0”. If your project.assets.json file includes this string then you have a dependency on the vulnerable package.

Fixing transitive dependencies (csproj/VS2017)

If you have not found any reference to Microsoft.AspNetCore.Mvc.Core/1.1.0 this means none of your direct dependencies depend on the vulnerable version of Microsoft.AspNetCore.Mvc.Core or you have already fixed the problem by updating the direct dependencies.

If your transitive dependency review found references to the vulnerable Microsoft.AspNetCore.Mvc.Core/1.1.0 you must add a direct dependency to the updated package to your csproj file to override the transitive dependency. Open your projectname.csproj file in your editor, or right click on the project in Visual Studio 2017 and choose Edit projectname.csproj from the content menu, where projectname is the name of your project. Look for PackageReference nodes, for example;

<Project ToolsVersion="15.0" Sdk="Microsoft.NET.Sdk.Web">
  <PropertyGroup>
    <TargetFramework>netcoreapp1.1</TargetFramework>
  </PropertyGroup>
  <PropertyGroup>
    <PackageTargetFallback>$(PackageTargetFallback);portable-net45+win8+wp8+wpa81;</PackageTargetFallback>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="Microsoft.AspNetCore" Version="1.1.0" />
    <PackageReference Include="Microsoft.AspNetCore.Mvc" Version="1.1.0" />
    <PackageReference Include="Microsoft.AspNetCore.StaticFiles" Version="1.1.0" />
  </ItemGroup>
  <ItemGroup>
    <DotNetCliToolReference Include="Microsoft.VisualStudio.Web.CodeGeneration.Tools" Version="1.0.0-msbuild3-final" />
  </ItemGroup>
</Project>

In the example csproj file above there are 3 PackageReference nodes. The results of our transitive package search showed us that our application depends on the vulnerable Microsoft.AspNet.Mvc.Core version 1.1.0. To fix this you must add a new direct dependency by adding it to the csproj file. You do this by adding a new PackageReference at the top of the PackageReference list, referring the fixed version. For example, to pull in the fixed version of Microsoft.AspNet.Mvc.Core, version 1.1.1 in the example csproj file it would be changed as follows:

<Project ToolsVersion="15.0" Sdk="Microsoft.NET.Sdk.Web">
  <PropertyGroup>
    <TargetFramework>netcoreapp1.1</TargetFramework>
  </PropertyGroup>
  <PropertyGroup>
    <PackageTargetFallback>$(PackageTargetFallback);portable-net45+win8+wp8+wpa81;</PackageTargetFallback>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="Microsoft.AspNetCore.Mvc.Core" Version="1.1.1" />
    <PackageReference Include="Microsoft.AspNetCore" Version="1.1.0" />
    <PackageReference Include="Microsoft.AspNetCore.Mvc" Version="1.1.0" />
    <PackageReference Include="Microsoft.AspNetCore.StaticFiles" Version="1.1.0" />
  </ItemGroup>
  <ItemGroup>
    <DotNetCliToolReference Include="Microsoft.VisualStudio.Web.CodeGeneration.Tools" Version="1.0.0-msbuild3-final" />
  </ItemGroup>

Once you have added the direct dependency reference save your csproj file.

If you are using Visual Studio save your updated csproj file and Visual Studio will restore the new package versions. You can see the restore results by opening the Output Window (Ctrl+Alt+O) and change the “Show output from” drop down to Package Manager.

If you are not using Visual Studio open a command line and change to your project directory. Execute the dotnet restore command to restore your new dependencies.

Rebuilding your application

Finally rebuild your application, test as you would do normally and redeploy using your favored deployment mechanism.

Support

Reporting Security Issues

  • If you have found a potential security issue in .NET Core please email details to secure@microsoft.com. Reports may qualify for the .NET Core Bug Bounty. Details of the .NET Core Bug Bounty including Terms and Conditions are at https://aka.ms/corebounty.

Microsoft Active Protections Program (MAPP)

To improve security protections for customers, Microsoft provides vulnerability information to major security software providers in advance of each monthly security update release. Security software providers can then use this vulnerability information to provide updated protections to customers via their security software or devices, such as antivirus, network-based intrusion detection systems, or host-based intrusion prevention systems. To determine whether active protections are available from security software providers, please visit the active protections websites provided by program partners, listed in Microsoft Active Protections Program (MAPP) Partners.

Feedback

Support

Disclaimer

The information provided in this advisory is provided "as is" without warranty of any kind. Microsoft disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a particular purpose. In no event shall Microsoft Corporation or its suppliers be liable for any damages whatsoever including direct, indirect, incidental, consequential, loss of business profits or special damages, even if Microsoft Corporation or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion or limitation of liability for consequential or incidental damages so the foregoing limitation may not apply.

Revisions

  • V1.0 (January 27, 2017): Advisory published.
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