Exploiting Kerberos RC4 Vulnerabilities to Spoof Windows PACs 🛡️

While the Active Directory implementation of Kerberos prefers to use cryptography based on AES, the deprecated Kerberos encryption type is still supported by default and widely used in practice. The property that RC4 derives its cryptographic keys from a user's NTLM hash is frequently exploited to authenticate without the original password (overpass-the-hash) or to efficiently brute-force service account passwords offline (Kerberoasting).No attacks were yet known that take advantage of the well-known weaknesses in Kerberos' RC4 implementation. Therefore I decided to take a look at this and quickly identified a relatively obvious flaw in the way it was used.However, turning this cryptographic flaw into a practical attack against Kerberos or Active Directory turned out to be far from trivial...

By: Tom Tervoort

Full Abstract and Presentation Materials:
https://www.blackhat.com/eu-22/briefings/schedule/#breaking-kerberos-rc-cipher-and-spoofing-windows-pacs-29181