Kerberoasting attacks are cyber-attacks that exploit the Kerberos authentication protocol, an industry-standard security model since the mid-1990s that gives hackers ample opportunities to exploit any vulnerabilities.
Kerberos is an authentication method that uses time-bound cryptographic messages to validate user identity, helping ensure that passwords don't travel across a network.
Kerberoasting attacks are security threats that exploit weaknesses in Kerberos authentication protocols, enabling hackers to gain entry to sensitive information of various organizations such as Microsoft, Apple, and NASA.
Authentication is a cornerstone of network security, enabling users to utilize their credentials securely when accessing servers and services. Historically, users logged onto computer systems by typing their password to gain entry to files, emails, etc. However, this method is far less secure than needed and allows attackers complete control of a system by taking over users' identities and taking control of systems remotely.
Kerberos uses tickets as a verification mechanism, using encrypted cryptographic algorithms to authenticate users. After being sent between the client and server, tickets are decrypted by the server, verifying whether their information matches what was contained within. This process ensures maximum file access validity for every authenticator within each ticket.
Kerberos relies on Key Distribution Centers (KDCs) as third-party authentication services, granting clients' requests to access certain services.
Once the KDC approves your request, they create a service session key for that user and send it back to you - your client can then use this to access services as long as its validity remains.
Therefore, Kerberos is an excellent solution for safeguarding communications between clients and servers, supported by many software applications and widely used as an authentication and authorization standard in IT environments.
But like any system, Kerberos can contain vulnerabilities to be exploited to compromise it. Luckily, these flaws are usually easy to mitigate; therefore, organizations must regularly evaluate the health of their Kerberos implementations.
One of the most prevalent vulnerabilities that can be exploited is "pass-the-ticket," in which an attacker forges and passes on an invalid service ticket, known as Silver Ticket, to a KDC server. Once they possess this fraudulent ticket, hackers gain direct access to services and resources in the domain where NTLM hashes were generated, allowing them to move laterally and vertically across networks.
Kerberoasting attacks?
Kerberos authentication protocol is designed to secure network access and client-server communications using symmetric key cryptography and an independent third party, the KDC, to authenticate users against various services on a network.
The authentication process begins when a client logs onto a Kerberos-enabled service and requests authentication from the KDC. When received, this request is reviewed against their database to validate if the client exists; once verified, if applicable, they receive a Ticket Granting Ticket (TGT) with a session key if applicable to them, and clients can then use these to decrypt a service ticket which application servers verify before giving access.
Kerberos authentication offers several advantages over password-based methods, the main one being its ability to avoid transmitting passwords over a network.
Another advantage is the reusable and durable authentication process provided by Kerberos, meaning users only need to authenticate once for all services on the network that rely on its protection.
Kerberos utilizes a central database to keep track of user identities and the systems and services they can authenticate. It provides effective access control as a reference point for logins and security policy enforcement.
If a system is compromised, attackers can leverage credentials stored in its database to gain unauthorized access. Standard methods against Kerberos authentication processes include falsified tickets, repeated password guessing attempts, and encryption downgrading malware.
An effective defense against Kerberoasting attacks is to update software that supports Kerberos regularly, so any new vulnerabilities are identified and addressed quickly so attacks are prevented.
Organizations should conduct regular audits of their authentication processes and implement policies to protect users' passwords from being misused by threat actors attempting to gain entry through authentication processes within an organization. Doing so will prevent threat actors from abusing this process to access other servers or resources.
There are various methods by which threat actors can exploit Kerberos, so auditors must comprehend its inner workings and identify attacks against it. Doing this will enable them to use these techniques appropriately during pen tests while also ensuring attackers don't exploit other security weaknesses within an organization.
Kerberoasting Attack Detection Strategies
Kerberos is an open-source protocol widely utilized by systems, including Apple OS, FreeBSD, UNIX, and Linux, to authenticate users to network services securely. SSO services use Kerberos to allow multiple services to share a single authentication token for user logins.
Kerberos provides secure storage for this information using symmetric key cryptography; passwords never pass over the network and are only accessible at an approved Key Distribution Center (KDC). Once authenticated, users are issued a service ticket that allows access to other kerberized services within their domain.
Cyber Attackers have various means to gain entry to a Kerberos session key and access resources or impersonate other users. A pass-the-ticket attack, for instance, where attackers use local admin credentials stolen by malware to forge fake service authentication tickets (SATs) they then submit back to KDCs as fake tickets, is one such method of gain.
An alternative method is a "pass-the-hash attack," in which an attacker obtains an individual's NTLM password hash and passes it back to the KDC to access resources or impersonate other users. While cyber attackers have used this attack for some time now, many still rely on it today.
To detect a kerberoasting attack, it is best to closely monitor network traffic for signs of malicious activity and adopt modern software that can identify vulnerabilities immediately and stop an attack before it takes place.
If your infrastructure is aged and malicious traffic increases dramatically, now might be the time to upgrade security measures to defend against new threats and stop damage caused by attacks such as Kerberoasting. Doing this will provide effective responses against any unauthorized access attempts and help prevent catastrophic attacks against your company.
Recognizing an attacker trying to use an exploited LDAP server or KDC to obtain user password hashes is key to avoiding kerberoasting attacks, a type of cybercrime often carried out by ransomware operators.
How to prevent Kerberoasting Attacks?
Kerberoasting is one of the many methods hackers employ to undermine Kerberos security. This type of cryptographic exploit involves stealing Ticket Granting Tickets (TGSs) to gain entry to an application service or domain account.
Kerberos is a network authentication protocol that utilizes tickets between client-server communication to authenticate and authorize users. Each ticket is encrypted using symmetric key cryptography - considered one of the safest forms of encryption, yet it still may be vulnerable to hacking attacks.
Physical security measures should be employed when protecting Kerberos servers. This may include running them on dedicated hardware without permitting other services to run on those machines and not storing users' passwords elsewhere.
Kerberos servers must also be regularly upgraded and backed up to prevent attackers from seizing them for misuse. This step becomes particularly essential when upgrading to a more recent version of Kerberos.
An additional method of protecting Kerberos involves synchronizing clocks on all servers - this allows the KDC to authenticate clients based on their system clock.
Kerberos servers consist of an Authentication Server (AS) and Ticket Granting Server (TGS). To gain access to services, clients contact the TGS and request a TGT number; this number contains information such as client ID, time and date stamp, as well as the network address of their client.
Once received by the client, a TGT is decrypted and compared against the secret key; access is granted for that service if it matches up.
If no match can be found, then a TGT is canceled and sent back to the KDC. This process continues until an acceptable match is found.
Recall that Kerberos clients can only access services using the TGTs they have received from the KDC, and failing to do so may prevent accessing those services and require changing passwords to regain access.
FAQ Section
A Kerberoasting Attack is a technique used to extract and crack service account passwords stored in a Windows Active Directory environment.
Attackers identify service accounts vulnerable to Kerberoasting, request a ticket-granting ticket (TGT), and then crack the encrypted passwords offline.
Kerberoasting exposes weak service account passwords, which can lead to unauthorized access, lateral movement, and data breaches within the compromised network.
Implement strong, unique passwords for service accounts, regularly rotate passwords, and monitor for abnormal activity in Active Directory logs.
Enforce the principle of least privilege, limit the number of service accounts, enable two-factor authentication, and use security tools that detect Kerberoasting attempts.
