Microsoft Security Advisory CVE-2018-8292: .NET Core Information Disclosure Vulnerability

[leecow]

Microsoft Security Advisory CVE-2018-8292: .NET Core Information Disclosure 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 security feature bypass vulnerability that exists when .NET Core when HTTP authentication information is inadvertently exposed in an outbound request that encounters an HTTP redirect. An attacker who successfully exploited this vulnerability could use the information to further compromise the web application.

The update addresses the vulnerability by correcting how .NET Core applications handles HTTP redirects.

System administrators running .NET Core 1.0 or .NET Core 1.1 applications must update their .NET Core runtimes to versions 1.0.13 and 1.1.10 then restart their applications. If installed applications target .NET Core 2.0, the applications must be migrated to 2.1 or newer and redeployed.

Developers must update their .NET Core SDK to versions 1.1.11 and migrate any .NET Core 2.0 or ASP.NET Core 2.0 applications to 2.1 then redeploy.

Mitigation factors

None

Affected software

Any .NET Core application that runs on a .NET Core 1.0.x runtime with a version number of 1.0.12 or lower, or a .NET Core application that runs on a .NET Core 1.1.x runtime with a version number of 1.1.9 or lower, or a .NET Core application that runs on a .NET Core 2.0.x runtime.

Additionally package authors should check their dependencies to ensure they aren't depending on a vulnerable version of the following package:

Package name	Vulnerable versions	Secure versions
System.Net.Http	2.0.20126.16343, 2.0.20505, 2.0.20710, 4.0.0, 4.1.0, 4.1.1, 4.1.2, 4.3.0, 4.3.1, 4.3.2, 4.3.3	4.3.4 or later

Advisory FAQ

How do I know if I am affected?

Any .NET Core application that runs on a .NET Core 1.0.x runtime with a version number of 1.0.12 or lower, or a .NET Core application that runs on a .NET Core 1.1.x runtime with a version number of 1.1.9 or lower, or a .NET Core application that runs on a .NET Core 2.0.x runtime.

To check the currently installed runtimes and SDKs with version 2.1 or later of .NET Core, open a command prompt and run the dotnet --info command. You should see an output similar to the following:

.NET Core SDK (reflecting any global.json):
 Version:   2.1.403
 Commit:    04e15494b6

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.17763
 OS Platform: Windows
 RID:         win10-x64
 Base Path:   C:\Program Files\dotnet\sdk\2.1.403\

Host (useful for support):
  Version: 2.1.5
  Commit:  290303f510

.NET Core SDKs installed:
  1.0.4 [C:\Program Files\dotnet\sdk]
  1.1.10 [C:\Program Files\dotnet\sdk]
  2.0.3 [C:\Program Files\dotnet\sdk]
  2.1.4 [C:\Program Files\dotnet\sdk]

.NET Core runtimes installed:
  Microsoft.AspNetCore.All 2.1.4 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.App 2.1.4 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 1.0.12 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 1.1.9 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.0.9 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.1.5 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]

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

If you don't see a runtime entry for 1.0.13 or 1.1.10, any .NET Core 1.x applications run on that computer are vulnerable.

If you don't have a 2.1 version of the runtime or SDK installed, you can produce the complete list of runtimes by performing a directory listing in the install root directories. The default root directories are listed in the following table:

Operating System	Location
Windows	C:\Program Files\dotnet\shared\Microsoft.NETCore.App\
macOS	/usr/local/share/dotnet/shared/Microsoft.NETCore.App/
Supported Linux platforms	/usr/share/dotnet/shared/Microsoft.NETCore.App/

Each runtime version is installed in its own directory, where the directory name is the version number. If you don't have a directory for 1.0.13, 1.1.10 then any application targeting versions 1.0 or 1.1 are vulnerable.

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.

How do I fix the vulnerability?

System administrators are advised to update their .NET Core runtimes to versions 1.0.13, 1.1.10 and install the latest 2.1 runtime, ensuring that any 2.0 applications are migrated to 2.1 as soon as possible.

Developers are advised to update their .NET Core SDK to versions 1.1.11 and migrate any .NET Core or ASP.NET Core 2.0 applications to 2.1 and redeploy.

Other Information

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.

Support

You can ask questions about this issue on GitHub in the .NET Core or ASP.NET Core organizations. These are located at https://github.com/dotnet/ and https://github.com/aspnet/, respectively. The Announcements repo for each product (https://github.com/dotnet/Announcements and https://github.com/aspnet/Announcements) will contain this bulletin as an issue and will include a link to a discussion issue. You can ask questions in the 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-2018-8292

Revisions

V1.0 (October 10, 2018): Advisory published.
Version 1.0
Last Updated 2018-10-10

[Sebazzz]

System.Net.Http is also available for full .NET framework. Is that version also affected?

[omajid]

If I do dotnet new web using a .NET Core 2.1.403 SDK targetting netcoreapp2.1, it produces a obj/project.assets.json that contains references to System.Net.Http/4.3.0. The table above says versions less than 4.3.4 are vulnerable. Is my version of System.Net.Http vulnerable? Apologies if this is a stupid question.

[rmkerr]

@Sebazzz we use a different HTTP stack on .NET Framework. The issue is not present there.

[rmkerr]

@omajid Not a stupid question :)

4.3.0 predates the fix, and is vulnerable.

[omajid]

@rmkerr Thanks. What do I need to do to resolve this issue in Runtime 2.1.5/SDK 2.1.403? Do I explicitly need to specify a version of System.Net.Http? The main post above says 2.1 is not vulnerable 😕

[leecow]

@omajid - the word I have from Nate and Wes is that this is a 'false positive'. The presence of System.Net.Http in the package graph of netcoreapp2.0 isn't the final determination of what is loaded at runtime. The version conflict resolution logic will prefer what is present in Microsoft.NETCore.App/2.1.5 (or latest patch release).

[omajid]

Thanks, @leecow.