Discovering Domains via a Time-Correlation Attack on Certificate Transparency

Many modern websites employ an automatic issuance and renewal of TLS certificates. For enterprises, there are DigiCert services. For everyone else, there are free services such as Let’s Encrypt and ZeroSSL.

There is a flaw in a way that deployment of TLS certificates might be set up. It allows anyone to discover all domain names used by the same server. Sometimes, even when there is no HTTPS there!

In this article, I describe a new technique for discovering domain names. Afterward, I show how to use it in threat intelligence, penetration testing, and bug bounty.

Continue reading

Exploiting Arbitrary Object Instantiations in PHP without Custom Classes

During an internal penetration test, I discovered an unauthenticated Arbitrary Object Instantiation vulnerability in LAM (LDAP Account Manager), a PHP application.

PHP’s Arbitrary Object Instantiation is a flaw in which an attacker can create arbitrary objects. This flaw can come in all shapes and sizes. In my case, the vulnerable code could have been shortened to one simple construction:

new $_GET['a']($_GET['b']);

That’s it. There was nothing else there, and I had zero custom classes to give me a code execution or a file upload. In this article, I explain how I was able to get a Remote Code Execution via this construction.

Continue reading

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.

Continue reading

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.

Continue reading