Dirk-jan Mollema

Dirk-jan Mollema

Hacker, red teamer, researcher. Likes to write infosec-focussed Python tools. This is my personal blog containing research on topics I find interesting, such as (Azure) Active Directory internals, protocols and vulnerabilities.

Looking for a security test or training? Business contact via outsidersecurity.nl

Recent Posts

Relaying Kerberos over DNS using krbrelayx and mitm6

11 minute read

One thing I love is when I think I understand a topic well, and then someone proves me quite wrong. That was more or less what happened when James Forshaw published a blog on Kerberos relaying, which disproves my conclusion that you can’t relay Kerberos from a few years ago. James showed that there are some tricks to make Windows authenticate to a different Service Principal Name (SPN) than what would normally be derived from the hostname the client is connecting to, which means Kerberos is not fully relay-proof as I assumed. This triggered me to look into some alternative abuse paths, including something I worked on a few years back but could never get to work: relaying DNS authentication. This is especially relevant when you have the ability to spoof a DNS server via DHCPv6 spoofing with mitm6. In this scenario, you can get victim machines to reliably authenticate...

NTLM relaying to AD CS - On certificates, printers and a little hippo

14 minute read

I did not expect NTLM relaying to be a big topic again in the summer of 2021, but among printing nightmares and bad ACLs on registry hives, there has been quite some discussion around this topic. Since there seems to be some confusion out there on the how and the why, and new attack vectors coming up fast now, I figured I’d write a short post with some more details and background. Hardly anything here is my own research, so I don’t take credit for any of this, but since these issues are “by design” and will likely not see a patch or significant change soon, they are quite relevant. That’s why I decided to write some Python tools around it and explain the process in this post. The tools are available on my GitHub.

Active Directory forest trusts part 2 - Trust transitivity and finding a trust bypass

24 minute read

In my first personal blog post in 2018 I wrote about Active Directory forest trusts and how they work under the hood. Part two of the series was since then promised but never delivered. I researched this topic again in 2019 and ended up finding a logic flaw which allowed the bypassing of the SID filtering mechanism and compromise hosts in a trusted forest. This flaw was patched in February 2020 and given CVE-2020-0665. Because of a global pandemic that cancelled most in-person conferences in 2020 I didn’t really get around to talk about this much even though it is one of my favorite finds to date. Under the motto “better late than never”, here is part 2 of the forest trust series, with the knowledge I’ve learned since then. Part of this content is also available as video on my YouTube channel.

A different way of abusing Zerologon (CVE-2020-1472)

17 minute read

In August 2020, Microsoft patched CVE-2020-1472 aka Zerologon. This is in my opinion one of the most critical Active Directory vulnerabilities of the past few years, since it allows for instant escalation to Domain Admin without credentials. The most straightforward way to exploit this involves changing the password of a Domain Controller computer account. This is a risky move and could potentially break things in the environment. In this blog we explore a new way to exploit this vulnerability, which though it has a few more prerequisites, is safer to use for security professionals assessing network security. We’ll also dive a bit more into the authentication protocols in Active Directory and how they can be tied in with the Zerologon vulnerability. While this is a different way of exploiting the vulnerability, it does not bypass the mitigations released, so if you have already installed the August 2020 patches, you are...

Digging further into the Primary Refresh Token

19 minute read

In my previous blog I talked about using the Primary Refresh Token (PRT). The PRT can be used for Single Sign On in Azure AD through PRT cookies. These cookies can be created by attackers if they have code execution on a victim’s machine. I also theorized that since the PRT and the cryptographic keys associated with it it are present on the victims device, they could be extracted from memory with the right tools. I wanted to further understand how the PRT works so I continued digging into it. Around the same time Benjamin Delpy took up my “challenge” of recovering PRT data from lsass with mimikatz. We combined forces and ended up with tooling that is not only able to extract the PRT and associated cryptographic keys (such as the session key) from memory, but can also use these keys to create new SSO cookies or modify existing...