ADCS - Certighost CDC Chase Certificate Request (CVE-2026-54121)

title: ADCS - Certighost CDC Chase Certificate Request (CVE-2026-54121)
id: c4a1f389-2e6b-4d9a-8f0c-b73e5a12d947
related:
    - id: 2a9e4f17-6c3b-4d8a-e1f0-b57c2d94a631
      type: similar
status: experimental
description: |
    Detects Active Directory Certificate Services (ADCS) certificate requests that include the
    'cdc' (Client DC) request attribute pointing to a domain or IP that is not a known Domain Controller.

    'cdc' is an optional MS-WCCE enrollment attribute designed for cross-domain/cross-forest
    scenarios where a client in a child domain tells the CA which DC to contact for identity
    lookups when the CA cannot reach that domain directly. Legitimate values are DC hostnames
    or IPs that resolve to a real Domain Controller computer object in AD with the
    SERVER_TRUST_ACCOUNT (0x2000) userAccountControl bit set.

    In an attack, the attacker sets cdc to a domain or IP they control so the CA connects to their
    rogue SMB and LDAP services instead of a real DC. The rogue server returns a forged DC
    identity which the pre-patch CA accepts without validation. A malicious event looks like:

        Requester: DOMAIN\GHOST<random>$
        Attributes: cdc:<attacker_ip>
                    rmd:<target_dc_fqdn>
        SubjectAlternativeName: DNS Name=<target_dc_fqdn>

    CVE-2026-54121 (Certighost) is the known exploit for this path. The July 2026 patch added
    _ValidateChaseTargetIsDC which rejects cdc values that do not resolve to a legitimate
    DC object in Active Directory before following the chase.
references:
    - https://github.com/aniqfakhrul/CVE-2026-54121
    - https://gist.github.com/H0j3n/a5ef2609b5f2944ac2390a191a534c26
author: Swachchhanda Shrawan Poudel (Nextron Systems)
date: 2026-07-27
tags:
    - attack.privilege-escalation
    - attack.credential-access
    - attack.t1649
    - cve.2026-54121
    - detection.emerging-threats
logsource:
    product: windows
    service: security
    definition: |
        This requires two independent controls on the CA server.
            (1) CA\AuditFilter must have bit 0x04 (AUDIT_CERTSRV_REQUESTFLAGS) set
                this instructs certsrv.exe to emit request/issuance events.
                Without this bit the CA never calls ReportEvent() for certificate operations, regardless of OS policy.
                    - Set via: certutil -setreg CA\AuditFilter 127 then net stop CertSvc; net start CertSvc.
            (2) The OS audit subcategory must be enabled to write those events into the Security log:
                auditpol /set /subcategory:"Certification Services" /success:enable.
        Note: GPO alone (without AuditFilter) is not sufficient.
detection:
    selection:
        EventID: 4886
        Attributes|contains: 'cdc:'
    filter_main_known_cdc:
        Attributes|contains|expand: '%known_cdcs%'  # should be populated with all known legitimate DC hostnames and IPs
    condition: selection and not 1 of filter_main_*
falsepositives:
    - Unknown
level: high