Locked KRBUACBypass: UAC Bypass By Abusing Kerberos Tickets

[itsMe]

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UAC Bypass By Abusing Kerberos Tickets

This POC is inspired by James Forshaw (@tiraniddo) shared at BlackHat USA 2022 titled “Taking Kerberos To The Next Level ” topic, he shared a Demo of abusing Kerberos tickets to achieve UAC bypass. By adding a KERB-AD-RESTRICTION-ENTRY to the service ticket, but filling in a fake MachineID, we can easily bypass UAC and gain SYSTEM privileges by accessing the SCM to create a system service. James Forshaw explained the rationale behind this in a blog post called “Bypassing UAC in the most Complex Way Possible!“, which got me very interested. Although he didn’t provide the full exploit code, I built a POC based on Rubeus. As a C# toolset for raw Kerberos interaction and ticket abuse, Rubeus provides an easy interface that allows us to easily initiate Kerberos requests and manipulate Kerberos tickets.

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Changelog v1.0

Now let’s take a look at the running effect, as shown in the figure below. First request a ticket for the HOST service of the current server through the asktgs function, and then create a system service through krbscm to gain the SYSTEM privilege.

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