AN ACE UP THE SLEEVE: DESIGNING ACTIVE DIRECTORY DACL BACKDOORS presented at blackhat 2017

by Will Schroeder, Andy Robbins,

Summary : Active Directory (AD) object discretionary access control lists (DACLs) are an untapped offensive landscape, often overlooked by attackers and defenders alike. The control relationships between AD objects align perfectly with the "attackers think in graphs" philosophy and expose an entire class of previously unseen control edges, dramatically expanding the number of paths to complete domain compromise.
While DACL misconfigurations can provide numerous paths that facilitate elevation of domain rights, they also present a unique chance to covertly deploy Active Directory persistence. It's often difficult to determine whether a specific AD DACL misconfiguration was set intentionally or implemented by accident. This makes Active Directory DACL backdoors an excellent persistence opportunity: minimal forensic footprint, and maximum plausible deniability.
This talk will cover Active Directory DACLs in depth, our "misconfiguration taxonomy," and enumeration/analysis with BloodHound's newly released feature set. We will cover the abuse of AD DACL misconfigurations for the purpose of domain rights elevation, including common misconfigurations encountered in the wild. We will then cover methods to design AD DACL backdoors, including ways to evade current detections, and will conclude with defensive mitigation/detection techniques for everything described.