Adversaries may modify access tokens to operate under a different user or system security context to perform actions and bypass access controls. Windows uses access tokens to determine the ownership of a running process. A user can manipulate access tokens to make a running process appear as though it is the child of a different process or belongs to someone other than the user that started the process. When this occurs, the process also takes on the security context associated with the new token.
An adversary can use built-in Windows API functions to copy access tokens from existing processes; this is known as token stealing. These token can then be applied to an existing process (i.e. Token Impersonation/Theft) or used to spawn a new process (i.e. Create Process with Token). An adversary must already be in a privileged user context (i.e. administrator) to steal a token. However, adversaries commonly use token stealing to elevate their security context from the administrator level to the SYSTEM level. An adversary can then use a token to authenticate to a remote system as the account for that token if the account has appropriate permissions on the remote system.
Any standard user can use the
runas command, and the Windows API functions, to create impersonation tokens; it does not require access to an administrator account. There are also other mechanisms, such as Active Directory fields, that can be used to modify access tokens.
Duqu examines running system processes for tokens that have specific system privileges. If it finds one, it will copy the token and store it for later use. Eventually it will start new processes with the stored token attached. It can also steal tokens to acquire administrative privileges.
HermeticWiper can use
KillDisk has attempted to get the access token of a process by calling
|M1026||Privileged Account Management||
Limit permissions so that users and user groups cannot create tokens. This setting should be defined for the local system account only. GPO: Computer Configuration > [Policies] > Windows Settings > Security Settings > Local Policies > User Rights Assignment: Create a token object.  Also define who can create a process level token to only the local and network service through GPO: Computer Configuration > [Policies] > Windows Settings > Security Settings > Local Policies > User Rights Assignment: Replace a process level token.
Administrators should log in as a standard user but run their tools with administrator privileges using the built-in access token manipulation command
|M1018||User Account Management||
An adversary must already have administrator level access on the local system to make full use of this technique; be sure to restrict users and accounts to the least privileges they require.
|ID||Data Source||Data Component||Detects|
|DS0026||Active Directory||Active Directory Object Modification||
Monitor for changes made to AD settings that may modify access tokens to operate under a different user or system security context to perform actions and bypass access controls.
Monitor executed commands and arguments for token manipulation by auditing command-line activity. Specifically, analysts should look for use of the
|DS0009||Process||OS API Execution||
Monitor for API calls, loaded by a payload, for token manipulation only through careful analysis of user network activity, examination of running processes, and correlation with other endpoint and network behavior. There are many Windows API calls a payload can take advantage of to manipulate access tokens (e.g.,
Monitor for executed processes that may modify access tokens to operate under a different user or system security context to perform actions and bypass access controls.
Query systems for process and thread token information and look for inconsistencies such as user owns processes impersonating the local SYSTEM account. Look for inconsistencies between the various fields that store PPID information, such as the EventHeader ProcessId from data collected via Event Tracing for Windows (ETW), Creator Process ID/Name from Windows event logs, and the ProcessID and ParentProcessID (which are also produced from ETW and other utilities such as Task Manager and Process Explorer). The ETW provided EventHeader ProcessId identifies the actual parent process.
|DS0002||User Account||User Account Metadata||
Monitor for contextual data about an account, which may include a username, user ID, environmental data, etc. that may modify access tokens to operate under a different user or system security context to perform actions and bypass access controls.