ADCS - Certighost Certificate Issued via CDC Chase (CVE-2026-54121)

title: ADCS - Certighost Certificate Issued via CDC Chase (CVE-2026-54121)
id: 8b7e2c54-1f93-4a6d-b8e0-3c9d7f25a168
status: experimental
description: |
    Detects successful issuance of an ADCS certificate where the request attributes include
    'cdc' (Client DC) or 'rmd' (Remote Domain) pointing to a non-DC domain or IP, confirming the
    CA's chase fallback path was taken against an attacker-controlled target.

    'cdc' directs the CA to an address for identity lookup; 'rmd' specifies the principal to
    look up there. In an attack (CVE-2026-54121, Certighost), cdc points to a rogue host that
    returns a forged DC identity. A successfully issued certificate at this stage means the
    attacker has obtained a cert carrying a Domain Controller's SID and DNS identity, enabling
    PKINIT authentication as that DC followed by DCSync replication.
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: 4887
        Attributes|contains:
            - 'cdc:'
            - 'rmd:'
    filter_main_known_cdc_ips:
        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