What it does. Detect DCSync attacks (MITRE ATT&CK T1003.006) by analyzing Windows Event ID 4662 (AccessMask 0x100) for DS-Replication-Get-Changes and DS-Replication-Get-Changes-All requests issued by non-domain-controller accounts. Use when hunting for DCSync credential theft, after detecting Mimikatz-class tooling, or during incident response and purple-team exercises involving Active Directory replication abuse. Part of mukul975/Anthropic-Cybersecurity-Skills (817 security skills) (mukul975/Anthropic-Cybersecurity-Skills).

Install

• npx skills add mukul975/Anthropic-Cybersecurity-Skills --skill hunting-for-dcsync-attacks, or copy the skill folder into ~/.claude/skills/hunting-for-dcsync-attacks/.
• Raw file: curl -sL https://raw.githubusercontent.com/mukul975/Anthropic-Cybersecurity-Skills/HEAD/skills/hunting-for-dcsync-attacks/SKILL.md

SKILL.md (verbatim)

name: hunting-for-dcsync-attacks
description: Detect DCSync attacks (MITRE ATT&CK T1003.006) by analyzing Windows Event ID 4662 (AccessMask 0x100) for DS-Replication-Get-Changes and DS-Replication-Get-Changes-All requests issued by non-domain-controller accounts. Use when hunting for DCSync credential theft, after detecting Mimikatz-class tooling, or during incident response and purple-team exercises involving Active Directory replication abuse.
domain: cybersecurity
subdomain: threat-hunting
tags:
- threat-hunting
- dcsync
- active-directory
- credential-access
- t1003.006
- mimikatz
- windows
- dfir
version: '1.0'
author: mahipal
license: Apache-2.0
d3fend_techniques:
- Application Protocol Command Analysis
- Network Isolation
- Network Traffic Analysis
- Client-server Payload Profiling
- Platform Monitoring
nist_csf:
- DE.CM-01
- DE.AE-02
- DE.AE-07
- ID.RA-05
mitre_attack:
- T1046
- T1057
- T1082
- T1083
- T1003

Hunting for DCSync Attacks

When to Use

• When hunting for DCSync credential theft (MITRE ATT&CK T1003.006)
• After detecting Mimikatz or similar tools in the environment
• During incident response involving Active Directory compromise
• When monitoring for unauthorized domain replication requests
• During purple team exercises testing AD attack detection

Prerequisites

• Windows Security Event Log forwarding enabled (Event ID 4662)
• Audit Directory Service Access enabled via Group Policy
• Domain Computers SACL configured on Domain Object for machine account detection
• SIEM with Windows event data ingested (Splunk, Elastic, Sentinel)
• Knowledge of legitimate domain controller accounts and replication partners

Workflow

1. Enable Auditing: Ensure Audit Directory Service Access is enabled on domain controllers.
2. Collect Events: Gather Windows Event ID 4662 with AccessMask 0x100 (Control Access).
3. Filter Replication GUIDs: Search for DS-Replication-Get-Changes and DS-Replication-Get-Changes-All.
4. Identify Non-DC Sources: Flag events where SubjectUserName is not a domain controller machine account.
5. Correlate with Network: Cross-reference source IPs against known DC addresses.
6. Validate Findings: Exclude legitimate replication tools (Azure AD Connect, SCCM).
7. Respond: Disable compromised accounts, reset krbtgt, investigate lateral movement.

Key Concepts

Tools & Systems

Output Format

Hunt ID: TH-DCSYNC-[DATE]-[SEQ]
Technique: T1003.006
Domain Controller: [DC hostname]
Subject Account: [Account performing replication]
Source IP: [Non-DC IP address]
GUID Accessed: [Replication GUID]
Risk Level: [Critical/High/Medium/Low]
Recommended Action: [Disable account, reset krbtgt, investigate]

Other files in this skill

• LICENSE
• references/api-reference.md
• scripts/agent.py

references/api-reference.md (verbatim)

DCSync Attack Detection Reference

Windows Event ID 4662

Directory Service Access event logged when an object in Active Directory is accessed.

Required Group Policy Configuration

Computer Configuration > Policies > Windows Settings > Security Settings >
Advanced Audit Policy Configuration > Audit Policies > DS Access >
Audit Directory Service Access: Success, Failure

Required SACL Configuration

Add "Domain Computers" to the SACL on the domain root object to detect machine account DCSync.

Key Detection GUIDs

AccessMask Value

0x100 (256 decimal) = Control Access - logged when access is allowed following extended rights verification.

Splunk Detection Query

index=wineventlog EventCode=4662
| where AccessMask="0x100"
| where match(Properties, "(?i)1131f6ad-9c07-11d1-f79f-00c04fc2dcd2") OR match(Properties, "(?i)1131f6aa-9c07-11d1-f79f-00c04fc2dcd2")
| where NOT match(SubjectUserName, "\\$$")
| eval is_dc=if(match(SubjectUserName, "(?i)(DC|AZUREADCONNECT)"), "legitimate", "suspicious")
| where is_dc="suspicious"
| stats count by SubjectUserName, SubjectDomainName, Computer, Properties

Elastic KQL Detection

event.code: "4662" AND winlog.event_data.AccessMask: "0x100" AND
winlog.event_data.Properties: (*1131f6ad-9c07-11d1-f79f-00c04fc2dcd2* OR *1131f6aa-9c07-11d1-f79f-00c04fc2dcd2*)
AND NOT winlog.event_data.SubjectUserName: *$

PowerShell Detection

# Query Event 4662 for replication GUID access
Get-WinEvent -FilterHashtable @{
    LogName='Security'; Id=4662
} | Where-Object {
    $_.Properties[8].Value -match '1131f6ad-9c07-11d1-f79f-00c04fc2dcd2' -and
    $_.Properties[1].Value -notmatch '\$$'
} | Select-Object TimeCreated,
    @{N='Account';E={$_.Properties[1].Value}},
    @{N='Domain';E={$_.Properties[2].Value}}

# List accounts with replication rights
Import-Module ActiveDirectory
(Get-Acl "AD:\DC=domain,DC=local").Access |
    Where-Object { $_.ObjectType -in @(
        '1131f6ad-9c07-11d1-f79f-00c04fc2dcd2',
        '1131f6aa-9c07-11d1-f79f-00c04fc2dcd2'
    )} | Select-Object IdentityReference, ActiveDirectoryRights

Attack Tools (for Detection Signatures)

# Mimikatz DCSync
lsadump::dcsync /domain:corp.local /user:krbtgt

# Impacket secretsdump.py
secretsdump.py -just-dc corp.local/admin:Password@dc01.corp.local

# Impacket - specific user
secretsdump.py -just-dc-user krbtgt corp.local/admin:Password@dc01.corp.local

MITRE ATT&CK Mapping

• Technique: T1003.006 - OS Credential Dumping: DCSync
• Tactic: Credential Access
• Platforms: Windows
• Data Sources: Active Directory: Active Directory Object Access, Network Traffic

Response Checklist

1. Disable compromised account immediately
2. Reset krbtgt password twice (12-hour interval between resets)
3. Revoke all Kerberos tickets (purge ticket cache)
4. Audit all accounts with replication rights on domain object
5. Review source host for additional compromise indicators
6. Check for persistence mechanisms (scheduled tasks, services, WMI)

Back to mukul975/Anthropic-Cybersecurity-Skills (817 security skills) or Agent skills.