Windows Integrity Levels

Windows Integrity Levels

A skill for understanding and working with Windows Mandatory Integrity Control (MIC) system.

Overview

Windows Vista and later use integrity levels to tag protected items. This prevents processes with lower integrity from modifying objects with higher integrity, regardless of traditional DACL permissions.

Integrity Level Hierarchy

From lowest to highest:

1. Untrusted - Anonymous logins (e.g., Chrome sandbox)
2. Low - Internet interactions, Protected Mode, Temporary Internet Folder
3. Medium - Default for standard users and most activities
4. High - Administrators (when elevated)
5. System - Windows kernel and core services
6. Installer - Special level above all others for uninstallation

Key Rules

• Objects cannot be modified by processes with lower integrity levels
• High integrity can modify lower levels; lower cannot modify higher
• Even Administrators group members run at Medium by default
• System level is out of reach even for administrators
• File system objects may have minimum integrity requirements
• All processes run under an integrity level

Checking Integrity Levels

Current Process Integrity

whoami /groups

Look for the Mandatory Level entry in the output.

Process Explorer Method

1. Open Process Explorer from Sysinternals
2. Right-click a process → Properties
3. View the Security tab
4. Check the integrity level in the security descriptor

File Integrity Level

icacls <filepath>

Look for Mandatory Label\<Level> Mandatory Level:(NW) in the output.

Modifying Integrity Levels

Set File Integrity Level

Must be run from an elevated (High integrity) console:

icacls <filepath> /setintegritylevel(oi)(ci) <Level>

Where <Level> is: Low, Medium, High, System

Important: A Medium integrity process cannot assign High integrity to objects.

Set Binary Integrity Level

icacls C:\Windows\System32\cmd.exe /setintegritylevel Low

Note: Setting a binary to High integrity does NOT make it run at High integrity automatically. The process inherits integrity from its parent.

Practical Implications

File System Access

When a file has a minimum integrity level:

• You must run at at least that integrity level to modify it
• Read access may still be possible from lower levels
• Traditional DACL permissions are secondary to integrity levels

Example:

# Create file as regular user (Medium integrity)
echo test > test.txt

# Set High integrity (requires admin)
icacls test.txt /setintegritylevel High

# Try to modify as regular user
echo new > test.txt  # Access is denied!

Process Access

• A process cannot write to another process with higher integrity
• Low integrity processes cannot open handles with full access to Medium integrity processes
• This is a key defense against privilege escalation

Binary Execution

• Setting a binary to Low integrity makes it run at Low integrity
• Setting a binary to High integrity does NOT make it run at High integrity
• Process integrity is inherited from the parent process

Security Best Practices

1. Run processes at the lowest integrity level possible - minimizes attack surface
2. Understand integrity boundaries - know what your process can and cannot access
3. Check integrity levels - use whoami /groups to verify your current level
4. Be aware of elevation - Administrator group ≠ High integrity by default

Common Use Cases

Privilege Escalation Assessment

When assessing for privilege escalation:

1. Check your current integrity level
2. Identify files/processes with lower integrity that you can modify
3. Look for files with High integrity that you cannot modify
4. Understand which processes you can inject into or manipulate

Security Hardening

To harden a system:

1. Set critical files to High integrity
2. Run untrusted applications at Low integrity
3. Verify integrity levels are properly configured
4. Monitor for integrity level violations

Tools

Included Scripts

• check-integrity.ps1 - Check integrity levels of files and processes
• set-integrity.ps1 - Set integrity levels on files (requires elevation)

External Tools

• Process Explorer (Sysinternals) - View process integrity levels
• whoami - Built-in Windows tool for checking groups and integrity
• icacls - Built-in Windows tool for managing file permissions and integrity

References

• Microsoft: Mandatory Integrity Control
• Sysinternals Process Explorer

Quick Reference