AS-REP Roasting

AS-REP Roasting targets Active Directory accounts that have Kerberos pre-authentication disabled. For those accounts the KDC will return an AS-REP — a blob encrypted with the account’s password hash — to anyone who asks, with no proof of identity, so an attacker can request it and crack it offline. Unlike Kerberoasting, it needs no valid domain login, which makes it an early move in most Active Directory assessments. The exchange happens over Kerberos on port 88, and a list of valid usernames — often gathered by password spraying — is all it takes to start.

How It Works

• Find the accounts. A single LDAP query lists users with the DONT_REQ_PREAUTH flag set — no privileges required.
• Request the AS-REP. Tools like GetNPUsers.py or Rubeus ask the KDC for the pre-auth-less response and pull the encrypted blob.
• Downgrade to RC4. Where AES isn’t enforced, the blob comes back as RC4 (etype 23), which cracks far faster.
• Crack offline. hashcat -m 18200 runs the blob against a wordlist — a weak password falls in minutes.
• No login needed. Because the request is anonymous, the attack can precede any credential theft in the kill chain.

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How to Detect It

• Alert on Event ID 4768 (TGT requested) with pre-authentication type 0 and RC4 encryption — the roasting signature.
• Watch for one host requesting AS-REPs for many distinct accounts in a short window.
• Plant a honeypot account with pre-auth disabled and never use it; any 4768 for it is a near-zero-false-positive alarm.

How to Defend Against It

• Enable Kerberos pre-authentication on every account — the setting that removes the attack entirely.
• Give any account that genuinely can’t use pre-auth a long random password so the offline crack fails.
• Enforce AES and retire RC4 to kill the fast-crack path, and keep such accounts out of privileged groups.

Log every pre-auth-less account and its time-to-crack under test, so the evidence lands in the pentest report instead of a scratch terminal you’ll lose.