ESC7 - Uwe Gradenegger

How securing printers can turn into a security disaster - and how the TameMyCerts Policy Module for Active Directory Certificate Services (ADCS) can prevent it

Nowadays, it is essential to protect the authentication of devices on the company network and administrative interfaces. As a rule, digital certificates are used for this purpose.

Printers therefore also generally require digital certificates in order to be operated securely. From a certain number of devices, there is no getting around automatic certificate distribution.

Some printer manufacturers offer centralized management solutions for certificate distribution.

Unfortunately, it has been shown time and again that the secure handling of digital certificates requires a great deal of knowledge, experience and care, which is often not the case.

How the TameMyCerts Policy Module for Active Directory Certificate Services (ADCS) can detect and prevent attacks against the ESC6 and ESC7 attack vectors

With the supposedly good intention of making it possible to issue such certificate requirements with a SAN, guess unfortunately much at many Instructions to set the flag on the certification authority EDITF_ATTRIBUTESUBJECTALTNAME2 to activate.

If this flag is activated, a very large attack surface is offered, as any applicant can now instruct the certification authority to issue certificates with any content. This type of attack is known in the security scene as ESC6 and ESC7 known.

Attack vector on Active Directory directory service via smartcard logon mechanism

In simple terms, public key cryptography can be reduced to the assumption that the private part of each key pair is known only to its owner.

A certification authority is responsible for the correct identification of users, computers or resources. Its issued certificates are therefore granted a trust status because all participants assume that their private key is known only to it.

If an attacker succeeds in gaining knowledge of a certification authority's private key, or at least Perform signatures using the private key, the integrity of the certification authority is no longer guaranteed.