Microsoft Security Advisory CVE-2020-1108 | .NET Core Denial of Service Vulnerability

[blowdart]

Microsoft Security Advisory CVE-2020-1108 | .NET Core Denial of Service Vulnerability

Executive summary

Microsoft is releasing this security advisory to provide information about a vulnerability in .NET Core. This advisory also provides guidance on what developers can do to update their applications to remove this vulnerability.

Microsoft is aware of a denial of service vulnerability which exists when .NET Core improperly handles web requests. An attacker who successfully exploited this vulnerability could cause a denial of service against a .NET Core web application. The vulnerability can be exploited remotely, without authentication.

A remote unauthenticated attacker could exploit this vulnerability by issuing specially crafted requests to the .NET Core application.

The update addresses the vulnerability by correcting how the .NET Core web application handles web requests.

Announcement

The original announcement for this issue can be found at dotnet/announcements#156

Mitigation factors

Microsoft has not identified any mitigating factors for this vulnerability.

Affected software

• Any .NET Core 2.1 application running on .NET Core 2.1.18 or lower
• Any .NET Core 3.1 application running on .NET Core 3.1.4 or lower
• Any .NET 5 application running on .NET 5 Preview 3 or lower

Please note that .NET Core 3.0 is now out of support and all applications should be updated to 3.1.

How do I know if I am affected?

If you have a runtime or SDK with a version listed in affected software you are exposed to the vulnerability.

How do I fix the issue?

To fix the issue please install the latest version of .NET Core. If you have multiple versions of .NET Core installed you will need to install multiple runtimes, or SDKs depending on what you have installed. If you have installed one or more .NET Core SDKs through Visual Studio, Visual Studio will prompt you to update Visual Studio which will also update your .NET Core SDKs.

You can list the versions you have installed by running the dotnet --info command. You will see output like the following;

.NET Core SDK (reflecting any global.json):
 Version:   3.1.100
 Commit:    cd82f021f4

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.18363
 OS Platform: Windows
 RID:         win10-x64
 Base Path:   C:\Program Files\dotnet\sdk\3.1.100\

Host (useful for support):
  Version: 3.1.0
  Commit:  65f04fb6db

.NET Core SDKs installed:
  3.0.101 [C:\Program Files\dotnet\sdk]

.NET Core runtimes installed:
  Microsoft.AspNetCore.App 3.1.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 3.1.0 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.WindowsDesktop.App 3.1.0 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

To install additional .NET Core runtimes or SDKs:
  https://aka.ms/dotnet-download

• For machines running .NET Core 2.1 you should download and install Runtime 2.1.19 or SDK 2.1.515 (for Visual Studio 2017 v15.9), 2.1.612 (for Visual Studio 2019 v16.0) or 2.1.807 (for Visual Studio 2019 v16.2 or later) from https://dotnet.microsoft.com/download/dotnet-core/2.1
• For machines running .NET Core 3.1 you should download and install Runtime 3.1.5 or SDK 3.1.105 (for Visual Studio 2019 v16.4) or 3.1.301 (for Visual Studio 2019 v16.5 or later) from https://dotnet.microsoft.com/download/dotnet-core/3.1
• For machines running .NET 5 Preview you should download and install .NET 5 Preview 4 when available from https://dotnet.microsoft.com/download/dotnet/5.0

If you have multiple affected versions you must update the runtime or SDKs for each version.

Once you have installed the updated runtime or SDK, restart your apps for the update to take effect.

Additionally, if you've deployed self-contained applications targeting any of the impacted versions, these applications are also vulnerable and must be recompiled and redeployed.

Other Information

Reporting Security Issues

If you have found a potential security issue in .NET Core, please email details to [email protected]. 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.

Support

You can ask questions about this issue on GitHub in the .NET Core GitHub organization. The main repos are located at https://github.com/dotnet/runtime and https://github.com/dotnet/aspnet/. The Announcements repo (https://github.com/dotnet/Announcements) will contain this bulletin as an issue and will include a link to a discussion issue. You can ask questions in the linked discussion issue.

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.

External Links

CVE-2020-1108

Revisions

V1.1 (June 9, 2020): Versions that contain the patch updated.
V1.0 (May 12, 2020): Advisory published.

Version 1.1

Last Updated 2020-06-09

[bgrainger]

The link under "External Links" is wrong: it should be "CVE-2020-1108" https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-1108 (not 1008).

[blowdart]

There has been an update to this issue. Last month's patches weren't complete, so the version numbers have been revised to show that this month's patch is the final patch for this issue.

[martincostello]

Any .NET Core 3.1 application running on .NET Core 3.1.5 or lower

Should this be "...3.1.4 or lower" or is there a 3.1.6 pending?

[HolisticDeveloper]

Presumably .NET Core versions that are EOL, such as 2.2 or 3.0, are also affected by this issue?

[michha]

Any .NET Core 3.1 application running on .NET Core 3.1.5 or lower

Should this be "...3.1.4 or lower" or is there a 3.1.6 pending?

Someone fixed it already in the announcement

V1.1 (June 9, 2020): Versions that contain the patch updated.

[KalleOlaviNiemitalo]

Does this issue affect ASP.NET Core 2.1 on .NET Framework; do I need to update any NuGet packages in such projects?

The .NET Core 2.1.19 fixes seem to be in System.IO.BinaryReader (commit) and System.Xml.XmlBufferReader (commit). I guess ASP.NET Core 2.1 on .NET Framework uses the corresponding .NET Framework types instead, so if it is vulnerable, then the fixes will have to come via .NET Framework updates such as KB4552925.