AS-REP Roasting

Executive Summary

AS-REP Roasting (T1558.004) is a MITRE ATT&CK technique associated with Credential Access. Preauthentication offers protection against offline Password Cracking.

Why Attackers Use It

Attackers use AS-REP Roasting because it provides a reliable way to advance their objective within the Credential Access tactic, often with a favorable balance of impact versus detectability on Windows environments. Defenders should assess this behavior in the context of the affected platform and adjacent activity rather than treating it as a standalone indicator.

MITRE Description

Adversaries may reveal credentials of accounts that have disabled Kerberos preauthentication by Password Cracking Kerberos messages.(Citation: Harmj0y Roasting AS-REPs Jan 2017)

Preauthentication offers protection against offline Password Cracking. When enabled, a user requesting access to a resource initiates communication with the Domain Controller (DC) by sending an Authentication Server Request (AS-REQ) message with a timestamp that is encrypted with the hash of their password. If and only if the DC is able to successfully decrypt the timestamp with the hash of the user’s password, it will then send an Authentication Server Response (AS-REP) message that contains the Ticket Granting Ticket (TGT) to the user. Part of the AS-REP message is signed with the user’s password.(Citation: Microsoft Kerberos Preauth 2014)

For each account found without preauthentication, an adversary may send an AS-REQ message without the encrypted timestamp and receive an AS-REP message with TGT data which may be encrypted with an insecure algorithm such as RC4. The recovered encrypted data may be vulnerable to offline Password Cracking attacks similarly to Kerberoasting and expose plaintext credentials. (Citation: Harmj0y Roasting AS-REPs Jan 2017)(Citation: Stealthbits Cracking AS-REP Roasting Jun 2019)

An account registered to a domain, with or without special privileges, can be abused to list all domain accounts that have preauthentication disabled by utilizing Windows tools like PowerShell with an LDAP filter. Alternatively, the adversary may send an AS-REQ message for each user. If the DC responds without errors, the account does not require preauthentication and the AS-REP message will already contain the encrypted data. (Citation: Harmj0y Roasting AS-REPs Jan 2017)(Citation: Stealthbits Cracking AS-REP Roasting Jun 2019)

Cracked hashes may enable Persistence, Privilege Escalation, and Lateral Movement via access to Valid Accounts.(Citation: SANS Attacking Kerberos Nov 2014)

Attack Flow

1. Attacker gains the prerequisite access or context described below.
2. Attacker executes AS-REP Roasting to achieve its tactical objective (Credential Access).
3. Resulting access/data/effect is leveraged to advance the broader attack chain (see Related Techniques).

Prerequisites

• Platform(s): Windows
• ATT&CK does not define one universal permission requirement for this technique. Establish the required access from the observed implementation and affected platform.

Common Tools

• Tool attribution is implementation-specific. Use ATT&CK procedure examples and local telemetry to identify the binaries, services, scripts, accounts, or cloud resources involved.

Commands

No universal command represents AS-REP Roasting. Capture the exact command line, arguments, parent process, account, host, and execution time from the investigated environment; do not operationalize unverified examples.

Network Traffic

• Network observability is implementation-dependent. Review DNS, proxy, firewall, flow, authentication, and packet telemetry around the activity window, then correlate remote endpoints and protocol behavior with host evidence.

Windows Events

Sysmon Events

Detection Opportunities

No MITRE detection guidance published for this technique.

Relevant ATT&CK Data Sources: N/A

Sigma Rules

A universal Sigma rule would create unreliable results because this technique has no single guaranteed observable. Build detection logic from a documented behavior and supported data source, scope it to the affected platform, and validate it against benign administrative activity before deployment.

Splunk Queries

Start with the data sources named in the detection section. Scope searches by asset, identity, and time window; correlate the primary behavior with preceding access and subsequent actions. A portable query is intentionally not provided where the technique lacks a universal schema or observable.

Investigation Workflow

1. Confirm that the observed behavior is consistent with AS-REP Roasting and rule out expected administrative or application activity.
2. Establish the first-seen time, initiating identity, source system, target system, and affected resources.
3. Collect relevant host, identity, network, cloud, and application telemetry for the surrounding time window.
4. Correlate parent and child activity, remote connections, file or configuration changes, and related ATT&CK techniques.
5. Determine scope by searching for the same observable across peer assets and identities.
6. Preserve volatile evidence and record confidence, assumptions, and telemetry gaps before containment.

Containment

1. Isolate affected host(s)/account(s) identified during investigation.
2. Revoke or rotate any credentials/tokens potentially exposed.
3. Apply the mitigations listed below where not already enforced.
4. Validate no related techniques (see Related Techniques) were chained against the same asset.

Mitigation

• M1047 -- Audit: Auditing is the process of recording activity and systematically reviewing and analyzing the activity and system configurations.
• M1027 -- Password Policies: Set and enforce secure password policies for accounts to reduce the likelihood of unauthorized access.
• M1041 -- Encrypt Sensitive Information: Protect sensitive information at rest, in transit, and during processing by using strong encryption algorithms.

Related Techniques

• T1558