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Introduction:
The recent escalation of the ESC1 attack vector demonstrates how a common Active Directory Certificate Services (AD CS) misconfiguration can serve as a primary entry point for threat actors. By exploiting vulnerable certificate templates, attackers can forge identity credentials with domain administrator privileges, bypassing traditional security controls and moving laterally with ease. This technique underscores the critical need for robust certificate authority governance and continuous monitoring of identity-based threats.
Learning Objectives:
- Understand the core components and exploitation path of the ESC1 AD CS vulnerability
- Learn to audit your environment for vulnerable certificate templates and misconfigurations
- Implement hardening measures and detection rules to protect against certificate-based attacks
You Should Know:
1. Understanding the ESC1 Attack Vector Fundamentals
The ESC1 attack exploits certificate templates that allow client authentication and permit low-privileged users to specify arbitrary Subject Alternative Names (SANs). When combined with enrollment rights, this enables attackers to request certificates for highly privileged accounts like Domain Administrators.
Step-by-step guide:
- Reconnaissance: Attackers first enumerate certificate templates and identify those with client authentication EKUs and SAN flexibility
- Template Identification: Locate templates where `msPKI-Certificate-Name-Flag` includes `ENROLLEE_SUPPLIES_SUBJECT` (allowing user-supplied SANs)
- Certificate Request: Use tools like Certify to request a certificate specifying a privileged account in the SAN field
- Authentication: Convert the certificate to a usable credential format and authenticate as the privileged account
2. Auditing Your Environment for Vulnerable Templates
PowerShell commands for identifying vulnerable certificate templates:
Get all certificate templates
Get-ADObject -LDAPFilter "(objectclass=pkicertificatetemplate)" -Properties Name, msPKI-Certificate-Name-Flag, msPKI-Enrollment-Flag, msPKI-RA-Signature, pKIExtendedKeyUsage, msPKI-RA-Application-Policies | Where-Object {
($<em>.'msPKI-Certificate-Name-Flag' -band 0x00000001) -and ENROLLEE_SUPPLIES_SUBJECT
($</em>.'pKIExtendedKeyUsage' -like "1.3.6.1.5.5.7.3.2") -and Client Authentication EKU
($_.'msPKI-Enrollment-Flag' -band 0x00000002) AUTO_ENROLLMENT check
}
Step-by-step guide:
- Run the PowerShell script against your domain to identify all templates
- Check for templates where low-privileged users have enrollment rights
- Verify if these templates allow SAN specification and contain client authentication EKU
4. Document all vulnerable templates for remediation
3. Exploitation Demonstration Using Certify
Certify command examples for exploitation:
Enumerate certificate templates Certify.exe find /vulnerable Request certificate for Domain Admin with SAN Certify.exe request /ca:CA01-DC01.corp.local\CORP-CA01-DC01-CA /template:VulnerableTemplate /altname:domainadmin Convert to PFX format for authentication Certify.exe pfx /cert:cert.pem /pvk:cert.pvk
Step-by-step guide:
1. Download and compile Certify from GitHub repository
- Execute enumeration to identify vulnerable templates in your environment
- Use the request function with /altname parameter to specify privileged account
- Convert the obtained certificate to PFX format for authentication
- Use Rubeus or similar tools to authenticate using the certificate
4. Hardening Certificate Template Configuration
Windows PowerShell commands for template hardening:
Disable SAN specification on vulnerable template
Set-ADObject "CN=WebServer,CN=Certificate Templates,CN=Public Key Services,CN=Services,CN=Configuration,DC=corp,DC=local" -Replace @{'msPKI-Certificate-Name-Flag' = 0}
Remove client authentication EKU from template
Set-ADObject "CN=WebServer,CN=Certificate Templates,CN=Public Key Services,CN=Services,CN=Configuration,DC=corp,DC=local" -Replace @{'pKIExtendedKeyUsage' = @('1.3.6.1.5.5.7.3.1')} Server Authentication only
Modify enrollment permissions
dsacls "CN=WebServer,CN=Certificate Templates,CN=Public Key Services,CN=Services,CN=Configuration,DC=corp,DC=local" /R "CORP\Domain Users"
Step-by-step guide:
- Identify all templates allowing SAN specification using ADSI Edit or PowerShell
2. Remove the ENROLLEE_SUPPLIES_SUBJECT flag from vulnerable templates
- Ensure templates used for device authentication don’t include client authentication EKU
- Review and restrict enrollment permissions to only necessary security principals
5. Implement role-based access control for certificate enrollment
5. Implementing Detection and Monitoring Controls
Sigma rules and Windows command-line detection:
Sigma rule for suspicious certificate requests title: Suspicious Certificate Template Request description: Detects certificate requests for templates vulnerable to ESC1 logsource: product: windows service: security detection: selection: EventID: 4886 Certificate Services received request TemplateName: - 'VulnerableTemplate' - 'WebServer' - 'User' condition: selection
PowerShell detection script:
Monitor certificate requests in real-time
Get-WinEvent -FilterHashtable @{LogName='Security'; ID=4886} -MaxEvents 100 |
Where-Object {$<em>.Message -like "ENROLLEE_SUPPLIES_SUBJECT"} |
ForEach-Object { Write-Warning "Suspicious certificate request detected: $($</em>.TimeCreated)" }
Step-by-step guide:
1. Deploy Sigma rules to your SIEM solution
- Enable auditing for Certificate Services (Event ID 4886, 4887)
3. Implement alerting for certificate requests specifying SANs
- Monitor for unusual enrollment patterns or requests from non-standard workstations
5. Establish baseline of normal certificate request behavior
6. Cloud Integration and Hybrid Environment Considerations
Azure AD PowerShell commands for monitoring:
Check for hybrid identity certificate-based authentication Get-MsolDomainFederationSettings -DomainName corp.local | Select-Object -ExpandProperty Certs Monitor for unusual certificate-based authentications Get-AzureADAuditSignInLogs -Filter "authenticationDetails/any(d:d/authenticationType eq 'certificate')" -Top 100
Step-by-step guide:
1. Audit hybrid identity configurations for certificate-based authentication
- Review Azure AD application registrations using certificate credentials
- Implement conditional access policies requiring MFA for certificate-based auth
- Monitor Azure AD sign-in logs for certificate authentication anomalies
- Ensure cloud security tools can detect on-premises AD CS attacks
7. Advanced Mitigation Using Certificate Authority Configuration
Command-line CA configuration hardening:
Disable vulnerable templates at CA level certutil -setreg CA\ValidityPeriodUnits 2 certutil -setreg CA\AuditFilter 127 Enable detailed CA auditing auditpol /set /subcategory:"Certification Authority" /success:enable /failure:enable
Step-by-step guide:
1. Access your Certificate Authority management console
- Disable or remove vulnerable templates from the CA issuance list
3. Implement certificate manager approval for sensitive templates
4. Configure CA event logging for comprehensive auditing
- Set appropriate certificate validity periods to limit exposure time
- Regularly backup and secure CA database and private keys
What Undercode Say:
- Identity is the New Perimeter: AD CS attacks demonstrate that certificate-based identity mechanisms have become the soft underbelly of enterprise security, often overlooked in traditional network-centric defense strategies.
- Configuration Drift Creates Attack Surface: The ESC1 vulnerability typically emerges from legitimate business requirements that gradually expand permissions without security review, highlighting the critical need for continuous configuration compliance monitoring.
The ESC1 attack pattern represents a fundamental shift in enterprise security paradigms. Where traditional attacks focused on credential theft or vulnerability exploitation, certificate-based attacks target the trust infrastructure itself. This creates a compounding risk where a single misconfiguration can undermine an entire identity and access management framework. Organizations must recognize that AD CS is not merely a convenience feature but a critical security component requiring the same rigor as domain controller hardening. The persistence of these vulnerabilities in production environments suggests that many organizations lack the specialized expertise needed to properly secure PKI implementations, creating a significant skills gap that adversaries are actively exploiting.
Prediction:
The ESC1 attack methodology will rapidly evolve into automated attack toolkits and become integrated into initial access brokers’ standard offerings within the next 12-18 months. As cloud identity integrations expand, we’ll see hybrid ESC1 attacks that leverage on-premises certificate vulnerabilities to pivot into cloud environments, potentially compromising Azure AD tenants and SaaS applications. The cybersecurity industry will respond with new certificate-focused EDR capabilities and specialized PKI monitoring solutions, but widespread adoption will lag behind attacker innovation, creating a window of significant risk for organizations with complex AD environments.
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IT/Security Reporter URL:
Reported By: Huykha From – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
