Kerberoasting without SPNs

Service principal names (SPNs) are records in an Active Directory (AD) database that show which services are registered to which accounts:

An example of an account that has SPNs

If an account has an SPN or multiple SPNs, you can request a service ticket to one of these SPNs via Kerberos, and since a part of the service ticket will be encrypted with the key derived from the account’s password, you will be able to brute force this password offline. This is how Kerberoasting works.

There is a way to perform the Kerberoasting attack without knowing SPNs of the target services. I’ll show how it could be done, how it works, and when it could be useful.

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Attacking MS Exchange Web Interfaces

During External Penetration Testing, I often see MS Exchange on the perimeter:

Examples of MS Exchange web interfaces

Exchange is basically a mail server that supports a bunch of Microsoft protocols. It’s usually located on subdomains named autodiscover, mx, owa or mail, and it can also be detected by existing /owa/, /ews/, /ecp/, /oab/, /autodiscover/, /Microsoft-Server-ActiveSync/, /rpc/, /powershell/ endpoints on the web server.

The knowledge about how to attack Exchange is crucial for every penetration testing team. If you found yourself choosing between a non-used website on a shared hosting and a MS Exchange, only the latter could guide you inside.

In this article, I’ll cover all the available techniques for attacking MS Exchange web interfaces and introduce a new technique and a new tool to connect to MS Exchange from the Internet and extract arbitrary Active Directory records, which are also known as LDAP records.

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