Sigma rule: Certificate Services Outbound SMB or LDAP Connection

A detection rule from the SigmaHQ repository, shown as its author published it. Dataset version ref-3b7b0c287ee2, updated 2026-07-29T00:00:00.000Z.

Rule

Title
Certificate Services Outbound SMB or LDAP Connection
Status
experimental
Level
high
Author
Swachchhanda Shrawan Poudel (Nextron Systems)
Date
2026-07-29
File
rules-placeholder/windows/network_connection/net_connection_win_certsvc_outbound_smb_ldap.yml
Commit
ccbb0369507f796db0b0ae6854c8a2be471b9d84

Detects the Windows Certificate Services process (certsrv.exe) initiating an outbound
network connection on port 445 (SMB) or 389 (LDAP) to a non-DC host. This behaviour is
inherently suspicious: under normal operation the CA resolves subject identities via local
RPC against the domain and never initiates outbound SMB or LDAP connections to arbitrary
hosts. Any such connection indicates the CA is being coerced into performing a remote
identity lookup against an attacker-controlled host.

The most direct known trigger is the CA chase fallback (EDITF_ENABLECHASECLIENTDC) where
a requester-supplied 'cdc' attribute causes the CA to open SMB and LDAP to a specified
address. CVE-2026-54121 (Certighost) exploits this path to redirect the CA to rogue LSA
and LDAP services that return a DC's identity, resulting in a forged DC certificate.
This rule is not limited to Certighost — any future vulnerability or misconfiguration
that causes certsrv.exe to make outbound SMB or LDAP connections is covered.

Log source

product
windows
category
network_connection

Detection

selection:
    Image|endswith: '\certsrv.exe'
    Initiated: 'true'
    DestinationPort:
        - 389
        - 445
filter_main_loopback:
    DestinationIp:
        - '127.0.0.1'
        - '::1'
        - '0:0:0:0:0:0:0:1'
filter_main_known_legit_ips:
    DestinationIp|expand: '%legit_ips%' # Including known legitimate IPs for the CA server (e.g. other DCs, LDAP servers, etc.)
condition: selection and not 1 of filter_main_*

False positives (as the rule lists them)

  • Unlikely

Tags

  • attack.privilege-escalation
  • attack.credential-access
  • attack.t1649

MITRE ATT&CK ids this rule names

Related rules

References

Read on 2026-11-03T00:58:21.399Z under licence sigma-drl-1.1@d5f4c36a from https://github.com/SigmaHQ/sigma/blob/ccbb0369507f796db0b0ae6854c8a2be471b9d84/rules-placeholder/windows/network_connection/net_connection_win_certsvc_outbound_smb_ldap.yml

Sources and licences

  • SigmaHQ

    "Certificate Services Outbound SMB or LDAP Connection" by Swachchhanda Shrawan Poudel (Nextron Systems) (SigmaHQ). Rule: https://github.com/SigmaHQ/sigma/blob/ccbb0369507f796db0b0ae6854c8a2be471b9d84/rules-placeholder/windows/network_connection/net_connection_win_certsvc_outbound_smb_ldap.yml.
    Licensed under the Detection Rule License (DRL) 1.1: https://github.com/SigmaHQ/Detection-Rule-License

    Detection Rule License (DRL) 1.1

Cite this page

Dragons Eye Ransomware Tracker, "Sigma rule: Certificate Services Outbound SMB or LDAP Connection",
entity page, dataset version ref-3b7b0c287ee2, updated 2026-07-29T00:00:00.000Z,
https://ransomware-tracker.com/detections/sigma/2a9e4f17-6c3b-4d8a-e1f0-b57c2d94a631 (accessed 2026-11-03).
Underlying source: SigmaHQ rule 2a9e4f17-6c3b-4d8a-e1f0-b57c2d94a631, commit ccbb0369507f796db0b0ae6854c8a2be471b9d84.

Pages change. The dataset version identifies the data, but no archive of old versions is kept, so this citation cannot be replayed later.