The goal of this blog post is to present a privilege escalation I found while working on ADCS. We will see how it is possible to elevate our privileges to NT AUTHORITY\SYSTEM from virtual and network service accounts of a domain-joined machine (for example from a webshell on a Windows server) using ADCS. I want to call this attack chain “CertPotato” as homage to other *Potato tools and as a way to better remember it. A popular technique for getting SYSTEM from a virtual or network service account is Delegate 2 Thyself by Charlie Clark. This technique involves using RBCD to elevate your privileges. In this article, I propose an alternative approach to become local SYSTEM using ADCS.

During an internal assessment, I performed an NTLM relay and ended up owning the NT AUTHORITY\SYSTEM account of the Windows server. Looking at the users connected on the same server, I knew that a domain administrator account was connected. All I had to do to compromise the domain, was compromise the account. This could be achieved by dumping the memory of the LSASS process and collecting their credentials or Kerberos TGT’s. Seemed easy until I realised an EDR was installed on the system. Long story short, I ended up compromising the domain admin account without touching the LSASS process. To do so, I relied on an internal Windows mechanism called token manipulation. The goal of this blog post is to present how I did it. We will see what access tokens are, what they are used for, how we can manipulate them to usurp legitimate accounts without touching LSASS and finally I will present a tool and a CrackMapExec module that can be used during such assessments. All the source code, binaries and CrackMapExec module can be found here https://github.com/sensepost/impersonate.