Imagine you just landed at your dream tourist destination and want to check in to your pre-booked hotel room. You confirm your identity by showing your passport to the receptionist. The receptionist accepts the proof and gives you the keycard to your room.
Your credentials are similar to a passport; they help confirm, or rather, authenticate, your identity to the server. Windows systems generate access tokens with your security context to give you access to protected resources, very similar to the hotel keycard issued by the receptionist. However, these access tokens can be stolen or manipulated.
Malicious actors want access to your protected resources and will try to impersonate you with stolen access tokens. This article is all about how attackers perform access token manipulation and how you can detect it in your IT environment.
Access tokens are usually issued to Windows processes. They contain a user ID, group ID, privilege, and other security information that cannot be tampered with. When a process tries to access a protected resource, Windows allows the process to do so only if its access token is validated with the access control list of the protected resource. The token that is attached to the initial process is inherited by all child processes. This is a privileged operation that can be carried out from a privileged context, such as an administrator account.
However, Windows has provisions that allow access tokens to be duplicated without any special privilege. For example, to restrict the access of a launched application, new tokens with a lower level of access rights, known as impersonation tokens, are created automatically. Attackers take advantage of these provisions to impersonate a user or system security context, bypass access controls, and perform malicious actions.
Access token manipulation is when an attacker uses built-in Windows API functions to copy access tokens from existing processes and modify them to suit their purpose. They may apply the stolen tokens to an existing process or use them under a different security context by creating a new process. The following Windows API calls can be used to steal and abuse access tokens: OpenProcess(), OpenProcessToken(), ImpersonateLoggedOnUser(), DuplicateTokenEx(), and CreateProcessWithTokenW().
The attacker would first compromise an administrator account from which they can make these API calls and steal access tokens. But attackers do not always require administrator privileges. They can use the RunAs/netonly command from any user account and access other computers in the network in a privileged context. Active Directory fields can also be used to modify access tokens.
Once attackers have these tokens, they access all permitted resources. They may establish access to remote systems or even compromise other systems in your network. Pass-the-hash, pass-the-ticket, and overpass-the-hash are some examples where access token manipulation is used for lateral movement.
Access token manipulation techniques are difficult to detect because they leave behind little evidence. Pass-the-ticket attacks are notoriously difficult to detect. However, some actions carried out during access token manipulation generate event logs.
Collecting system event logs and sifting through them for suspicious log patterns can help discover indicators of compromise for some access token manipulation techniques, as tabulated below.
|Indicators of compromise at endpoints
|Check your endpoint logs for:
|Indicators of compromise at endpoints
In short, this is where you can begin to increase your chances of detecting access token manipulation in your environment:
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