Windows Access Tokens

A guide to understanding and analyzing Windows access tokens for security assessments and privilege escalation research.

What Are Access Tokens

Each user logged onto a Windows system holds an access token containing security information for that logon session. The system creates this token when the user logs on, and every process executed on behalf of the user has a copy of the access token.

The token identifies:

• The user
• The user's groups
• The user's privileges
• A logon SID (Security Identifier) for the current logon session

Enumerating Access Tokens

Using whoami

The primary command for viewing token information:

whoami /all

This displays:

• User Information: Username and SID
• Group Information: All groups the user belongs to with their SIDs and attributes
• Privileges Information: All privileges with their state (Enabled/Disabled)

Using Process Explorer

From Sysinternals:

1. Select the target process
2. Access the "Security" tab
3. View the token details

Local Administrator Tokens

When a local administrator logs in, two access tokens are created:

1. One with administrator rights
2. One with normal (non-administrator) rights

By default, when this user executes a process, the one with regular rights is used. When the user tries to execute anything as administrator ("Run as Administrator"), UAC will prompt for permission.

Credential Impersonation

Creating New Logon Sessions

If you have valid credentials for another user, create a new logon session:

runas /user:domain\username cmd.exe

Network-Only Credentials

The access token has a reference to logon sessions inside LSASS, useful for network object access. Launch a process using different credentials for network services only:

runas /user:domain\username /netonly cmd.exe

This is useful when you have credentials to access network objects but those credentials aren't valid on the current host.

Token Types

Primary Token

• Serves as a representation of a process's security credentials
• Creation and association require elevated privileges
• Typically created by an authentication service
• Associated with the user's OS shell by a logon service
• Processes inherit the primary token of their parent process at creation

Impersonation Token

Empowers a server application to adopt the client's identity temporarily. Four levels of operation:

Level	Description
Anonymous	Grants server access akin to an unidentified user
Identification	Allows server to verify client identity without using it for object access
Impersonation	Enables server to operate under the client's identity
Delegation	Similar to Impersonation but extends identity assumption to remote systems, preserving credentials

Token Impersonation Techniques

Using Metasploit Incognito Module

If you have sufficient privileges, you can:

• List available tokens
• Impersonate other tokens
• Perform actions as if you were the other user
• Escalate privileges using this technique

Token Privileges

Token privileges can be abused for privilege escalation. Key resources:

• Priv2Admin: https://github.com/gtworek/Priv2Admin - Comprehensive list of token privileges and definitions
• Medium Tutorial Part I: Understanding and Abusing Process Tokens
• Medium Tutorial Part II: Understanding and Abusing Access Tokens

Practical Workflow

When analyzing Windows access tokens:

1. Enumerate current token: Run

   whoami /all

   to see groups and privileges
2. Identify privilege state: Note which privileges are Enabled vs Disabled
3. Check for admin tokens: If local admin, understand the dual-token system
4. Look for impersonation opportunities: Check for available tokens to impersonate
5. Research privilege abuse: Cross-reference enabled privileges with known escalation techniques

Key Commands Reference

# View full token information
whoami /all

# View current user
whoami

# View current user and groups
whoami /groups

# Run as different user
runas /user:domain\username cmd.exe

# Run with network-only credentials
runas /user:domain\username /netonly cmd.exe

Security Considerations

• Access tokens are fundamental to Windows security
• Understanding token mechanics is essential for security assessments
• Token impersonation requires appropriate privileges
• Always operate within authorized security testing boundaries
• Document findings and privilege escalation paths for remediation