SystemCollector

PoC for Privilege Escalation in Windows 10 Diagnostics Hub Standard Collector Service

Affected Products

• Windows 10
• Windows Server
• Windows Server 2016
• Visual Studio 2015 Update 3
• Visual Studio 2017

Summary

The Diagnostics Hub Packaging library, used by Windows Standard Collector Service, can be forced to copy an arbitrary file to an arbitrary location due to lack of client impersonation in DiagnosticsHub.StandardCollector.Runtime.dll.

Here is a detailed write-up on how this vulnerability was found and exploited: Privilege Escalation Vulnerability in Windows Standard Collector Service.

Technical Details

The Standard Collector Service allows for a several values to be defined when configuring a diagnostics session, including the scratch directory and session ID. The session ID can be any GUID and the scratch directory can be any location the user has write permissions too. If the collection session is configured with an ID of c13851b2-b1e1-438f-bf73-949df897f1bf and a scratch path of C:\Users\Bob\AppData\Local\Temp\Microsoft\F12\perftools\visualprofiler\, the following events occur when calling the GetCurrentResult method of the ICollectionSession object:

1. An Event Trace Log (.etl) file is created in the scratch path: C:\Users\Bob\AppData\Local\Temp\Microsoft\F12\perftools\visualprofiler\c13851b2-b1e1-438f-bf73-949df897f1bf.1.m.etl
2. A Report folder is also created in the scratch path: C:\Users\Bob\AppData\Local\Temp\Microsoft\F12\perftools\visualprofiler\Report.c13851b2-b1e1-438f-bf73-949df897f1bf.1
3. A folder with a random GUID is created in the report folder: C:\Users\Bob\AppData\Local\Temp\Microsoft\F12\perftools\visualprofiler\Report.c13851b2-b1e1-438f-bf73-949df897f1bf.1\EAD6A227-31D4-4EA2-94A9-5DF276F69E65

These folders and ETL files are created by the collector service for the .diagsession package that is normally created when a session has ended. Calling the Stop method on the ICollectionSession object will cause the collector service to commit the diagnostics package by calling Microsoft::DiagnosticsHub::Packaging::DhPackageDirectory::CommitPackage. The CommitPackage function will copy or move the original {scratch path}\c13851b2-b1e1-438f-bf73-949df897f1bf.1.m.etl file to the random GUID folder: {scratch path}\Report.c13851b2-b1e1-438f-bf73-949df897f1bf.1\EAD6A227-31D4-4EA2-94A9-5DF276F69E65\c13851b2-b1e1-438f-bf73-949df897f1bf.1.m.etl

The copy/move operation triggered by the CommitPackagingResult function in DiagnosticsHub.StandardCollector.Runtime.dll, is performed without impersonating the user (unlike the initial file/folder creation), leading to a possible TOCTOU issue if the target folder is replaced with a mount point that redirects the copy to an arbitrary location. To exploit this issue in a useful way, an attacker would need to swap the contents of the ETL file before it is copied. This can be done by beating the race condition with an OpLock after the file handle has been released by the service.

Although we don't fully control the name of the .etl file that is copied, we can use the object directory symlink trick to control it. The mount point+symlink setup would look something like this:

• Mount point: {scratch path}\Report.c13851b2-b1e1-438f-bf73-949df897f1bf.1\EAD6A227-31D4-4EA2-94A9-5DF276F69E65\ -> \RPC Control\
• Symlink: \RPC Control\c13851b2-b1e1-438f-bf73-949df897f1bf.1.m.etl -> C:\Windows\System32\anything.dll

Having control of the file contents, copy location, and file name gives an attacker numerous DLL loading possibilities. However, the included PoC demonstrates how control of the filename is not needed since the collector service happily load a DLL with any filename, as long as it is in C:\Windows\System32 or C:\Windows\System32\DiagSvcs directory. This is done by starting a new collector session with an agent that has an assembly name matching the name of the copied DLL c13851b2-b1e1-438f-bf73-949df897f1bf.1.m.etl.

The included PoC is a VS solution with a C++ DLL project for the notepad.exe popping payload and a C# project to interact with the service and exploit the vulnerability with the NtApiDotNet library.

Steps to reproduce:

1. Build Visual Studio Solution
2. Execute SystemCollector.exe as a normal user

Expected Result:

The package commit operation impersonates the user and fails when trying to copy the file.

Observed Result:

The file is copied to the mount point target folder C:\Windows\System32, then loaded as a collector agent, and finally, notepad.exe is spawned as SYSTEM privileges.

Additional References

• https://www.atredis.com/blog/cve-2018-0952-privilege-escalation-vulnerability-in-windows-standard-collector-service
• https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2018-0952
• https://github.com/atredispartners/advisories/blob/master/ATREDIS-2018-0004.md