Coercing Authentication with Coercer and PetitPotam

Legal Notice: This skill is for authorized security testing and educational purposes only. Authentication coercion combined with NTLM relay can yield domain compromise. Use only against systems you own or have explicit written authorization to test. Unauthorized use is illegal.

Overview

Many Windows RPC interfaces expose methods that take a UNC path and cause the receiving server to authenticate to that path using its machine account. An attacker who can reach these interfaces can force a target (commonly a Domain Controller) to authenticate to an attacker-controlled host. On its own this is "Forced Authentication"; combined with an NTLM relay, the coerced machine credential is relayed to a service that does not enforce signing/EPA, most famously AD CS Web Enrollment (ESC8), yielding a certificate for the Domain Controller and ultimately domain compromise.

PetitPotam (Gilles Lionel / topotam) abuses the MS-EFSR (Encrypting File System Remote Protocol) EfsRpcOpenFileRaw / EfsRpcEncryptFileSrv methods. Coercer (p0dalirius) generalizes the technique: it is a Python tool that automatically coerce…