Recently SPECTEROPS announced the release of Bloodhound 3.0 with three new attack methods — gMSA Control, OU Control & SID History. This article discusses how one can protect one’s Active Directory from these new attack methods.
Ask any Active Directory admins, and they would agree that service accounts have always been a problem from all aspects, including Manageability, Accountability, and, most importantly, Security. In every IT audit, Service Accounts are one of the top risks that auditors flag because passwords do not expire, unconstrained delegation happens, the accounts have extended privileges, and many other reasons. Making things worse is a new Kerberos attack method researchers recently discovered called a Silver Ticket attack. In 2012 Microsoft came up with a new concept called gMSA, which addressed most of the problems mentioned above. Domain controllers manage the passwords, which by default, change every 30 days automatically, uses 128-character strong passwords, and eliminates Silver Ticket attacks.
Recently one of the Bloodhound developers posted a tool (GMSAPasswordReader) on GitHub, which can read the password blob from a gMSA account. The tool can retrieve the NT hash of the gMSA account, which attackers can reuse. This article does not discuss the attack method, as the authors of Bloodhound have already documented it. It instead looks at what measures one can take to protect gMSA accounts.