discusses the services that Kerberos provides and how these fit into application access control. If an attacker gets the hash of any user, he could impersonate him against the KDC and then gain access to several services. After that, the KDC will respond with a KRB_AS_REP message, which will contain some information encrypted with the user key. Before learning how Kerberos works, it is important to learn the following terms. The weakest link in the Kerberos chain is the password. We will be adding more posts about kerberos in the coming days. Thank you!! This due to the fact that in many occasions it is not clear why some techniques works or not. TGT: A special ticket which contains the session key for communication between the client machine and the central KDC server. Why Kerberos is needed.
TGS: Ticket Granting Server: this is mostly the same central server (KDC server), it grants the tickets for a service. KDC: Key distribution Centre, this will be the server which we call the middle man server or the central server arbitrator, which issues the keys for the communication. All the same, on some occasions the owner of service is a normal user account. In kerberos infrastructure user login credentials are stored in the central server as mentioned before. Step4: The TGT recieved by the client from the KDC server will be stored in the cache for use for the session duration.
Kerberos uses a trusted third party or call a middle man server, for authentication. How to bypass disable_functions and open_basedir, Persistence in WordPress using backdoors in SQL. Step5: Now the client has got TGT in hand. Ports used by Kerberos are UDP/88 and TCP/88, which should be listen in KDC (explained in next section).
Passwords can be brute-force cracked or stolen by phishing attacks. Silver Ticket is similar, however, the built ticket is a TGS this time. In order to use it, user must send to the AP a KRB_AP_REQ message: After that, if user privileges are rigth, this can access to service. If you have any doubt about the topic which it is not well explained, do not be afraid on leave a comment or question about it. Kerberos uses differents kinds of messages. Before biginning with this post it will be an added advantage, to go through, Kerberos is an authentication system developed as part of athena project in MIT. In this regard, it is necessary to obtain the NTLM hash of krbtgt account. Editorial Sibex. ASREPRoast is similar to Kerberoasting, that also pursues the accounts passwords cracking. In this platform, Kerberos provides information about the privileges of each user, but it is responsability of each service to determine if the user has access to its resources. Kerberos has two purposes: security and authentication. If suppose the client needs to communicate with some service on that network, the client will ask the KDC server, for a ticket for that specific service with the help of TGT. In the context of Kerberos this is known as Overpass The Hash o Pass The Key. In this post we will try to understand some basic concepts of Kerberos. Step2: Kdc server searches the principal name in the database, on finding the principal, a TGT is generated by the KDC, which will be encrypted by the users key, and send back to the user. An important fact to note here is that, the client machine stores its key on its own machine only and this is never transmitted over wire. As such, a plan for integrating Kerberos into an application should carefully consider how these services are provided. From the different versions available in kerberos, version 1 to 3 were never released for public use as they were mainly internal releases. Domain Controller) as the default authentication protocol when joining a client to a Windows domain.
However, the computer passwords are very complex, thus, it is not useful to try to crack those. Thanks for the basic information, its very useful for a beginner. Due to this Kerberos is responsible for providing encryption. Therefore, after a long journey of diving into the documentation and several posts about the topic, we’ve tried to write in this post all the important details which an auditor should know in order to understand how take advantage of Kerberos protocol. And kerberos is based upon. How Does SSL/TLS Chain Certificates and Its Validation work? The principal, is sent to KDC server for login, and the KDC server will provide TGT in return(this request to the KDC server can be sent by the login program or we can also use kinit program) . More articles in this series about Kerberos, https://msdn.microsoft.com/en-us/library/cc233855.aspx, https://msdn.microsoft.com/en-us/library/cc223948.aspx, https://www.roguelynn.com/words/explain-like-im-5-kerberos/, https://msdn.microsoft.com/en-us/library/ms677949(v=vs.85).aspx, https://technet.microsoft.com/en-us/library/dbf0cdec-d72f-4ba3-bc7a-46410e02abb0, https://blog.gentilkiwi.com/securite/mimikatz/overpass-the-hash, https://blog.gentilkiwi.com/securite/mimikatz/pass-the-ticket-kerberos, https://blog.gentilkiwi.com/securite/mimikatz/golden-ticket-kerberos, https://www.beneaththewaves.net/Projects/Mimikatz_20_-_Golden_Ticket_Walkthrough.html, https://files.sans.org/summit/hackfest2014/PDFs/Kicking%20the%20Guard%20Dog%20of%20Hades%20-%20Attacking%20Microsoft%20Kerberos%20%20-%20Tim%20Medin(1).pdf, https://room362.com/post/2016/kerberoast-pt1/, https://room362.com/post/2016/kerberoast-pt2/, https://www.harmj0y.net/blog/activedirectory/roasting-as-reps/, https://passing-the-hash.blogspot.com.es/2014/09/pac-validation-20-minute-rule-and.html, https://blogs.msdn.microsoft.com/openspecification/2009/04/24/understanding-microsoft-kerberos-pac-validation/, https://gallery.technet.microsoft.com/Reset-the-krbtgt-account-581a9e51, https://www.microsoft.com/en-us/download/details.aspx?id=36036, https://speakerdeck.com/ropnop/fun-with-ldap-kerberos-and-msrpc-in-ad-environments?slide=58. Kerberos (III): How does delegation work?
This web use cookies. Having this knowledge allows to know when to use any of those attacks in a pentest. On most computer systems, a password is used to prove a user's identity; on a distributed network system, like Athena, this password must be transmitted over the network, from the workstation being used, to any other machines containing files or programs the user wants access to. User hashes can be extracted from SAM files in workstations or NTDS.DIT file of DCs, as well as from the lsass process memory (by using Mimikatz) where it is also possible to find cleartext passwords. The TGT only can be invalidate if this expires or krbtgt account changes its password. These are the following: There are several structures handled by Kerberos, as tickets. authentication server (AS) A server that issues tickets for a desired service which are in turn given to users for access to the service. http://www.slashroot.in/how-install-and-configure-kerberos-server. Autores: S. Anson , S. Bunting, R. Johnson y S. Pearson.
In this section several components of Kerberos environment will be studied. Firstly, user must get a TGT from KDC. Below is shown a summary of message sequency to perform authentication: In this section, the sequency of messages to perform authentication will be studied, starting from a user without tickets, up to being authenticated against the desired service. The following posts will show how to perform these attacks in a practical way and also how delegation works. Push Notification Authentication (Push Authentication), Elliptic Curve Digital Signature Algorithm (ECDSA), Active Directory Federation Services (AD FS), Security Assertion Markup Language (SAML), Security Information and Event Management (SIEM), Active Directory Certificate Services (AD CS), Stateless Authentication (Token-based Authentication), Client to Authenticator Protocol (CTAP/CTAP2), System for Cross-Domain Identity Management (SCIM), Challenge Handshake Authentication Protocol (CHAP), Salted Challenge Response Authentication Mechanism (SCRAM), Representational State Transfer (RESTful API), Lightweight Directory Access Protocol (LDAP), Defense Federal Acquisition Regulations Supplement (DFARS), National Institute of Standards and Technology (NIST), Center of Internet Security Controllers (CIS Controllers), Health Insurance Portability and Accountability Act (HIPAA), Payment Card Industry Data Security Standard (PCI DSS), General Data Protection Regulation (GDPR), Address Resolution Protocol Poisoning (ARP Poisoning), System for Cross-Domain Identity Management, Challenge Handshake Authentication Protocol, Salted Challenge Response Authentication Mechanism, Authentication Trends - Getting Beyond First Based Identification, LDAP, Active Directory and Federated Identity: What You Need to Know. An alternative is getting the ticket from lsass process memory, where also reside the session key. Nevertheless, it is not possible to sign correctly the PAC without krbtgt key. We also share information about your use of our site with advertising, analytics partners and with online chat services. It is better to obtain a TGT, due to TGS only can be used against one service. The objective of Golden Ticket is to build a TGT. This also happens in case of krbtgt account, therefore, TGT is not crackable neither. If is the case, which not usually happens, the AP will verify the PAC against the KDC. Ports used by Kerberos are UDP/88 and TCP/88, which should be listen in KDC (explained in next section). … And also, if mutual authentication is needed it will respond to user with a KRB_AP_REP message.
You can find the kerberos config guides in the below posts. Based on previous explained authentication process the attacks oriented to compromise Active Directory will be explained in this section. So its a tedious job to migrate all login credentials from local machines /etc/passwd and /etc/shadow files to the central server. Principal: this is the name used by the kerberos central server to call users, service name etc. Attacking Kerberos: Kicking the Guard Dog of Hades: Mitigating Pass-the-Hash (PtH) Attacks and Other Credential Theft: Fun with LDAP, Kerberos (and MSRPC) in AD Environments: Kerberos (I): How does Kerberos work? The popular Pass The Hash (PTH) attack consist in using the user hash to impersonate the specific user. Since the Kerberos authentication server maintains a database of passwords (encryption keys) for all the users at a site, it is extremely important that it be installed on a carefully protected and physically secure machine. It is possible to services to verify the PAC by comunicating with the KDC, although this does not happens often. With SSO you prove your identity once to Kerberos, and then Kerberos passes your TGT to other services or machines as proof of your identity. The Kerberos protocol uses a symmetric key derived from the user password to securely exchange a session key for the client and server to use.