CWE-1299: Missing Protection Mechanism for Alternate Hardware Interface

What is Missing Protection Mechanism for Alternate Hardware Interface?

• Overview: Missing Protection Mechanism for Alternate Hardware Interface is a vulnerability where alternate paths to control-protected assets are not secured, allowing attackers to bypass existing security measures that only protect the main access path.

• Exploitation Methods:

• Attackers can exploit this vulnerability by accessing unprotected shadow or mirror registers.
• Common techniques include using alternate interfaces like UART, SMBUS, or USB to access assets protected only through primary interfaces such as PCIe.

• Security Impact:

• Direct consequences include unauthorized access and manipulation of protected assets.
• Potential cascading effects involve further system compromise due to altered or stolen data.
• Business impact could include data breaches, loss of intellectual property, and damage to reputation.

• Prevention Guidelines:

• Ensure all access paths to sensitive assets are protected, not just the primary interface.
• Implement comprehensive access controls on shadow and mirror registers.
• Use security best practices such as regular security audits and penetration testing.
• Leverage hardware security features and tools to monitor and restrict access across all interfaces.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Not Language-Specific

Affected Technologies: Microcontroller Hardware, Processor Hardware, Bus/Interface Hardware, Not Technology-Specific

Vulnerable Code Example

Python Example

class HardwareController:
    def __init__(self):
        self._primary_interface = "ProtectedAccess"
        self.alternate_interface = "UnprotectedAccess"  # Publicly accessible, lacks protection
    
    def access_hardware(self):
        # Only protect primary interface access
        if self._primary_interface == "ProtectedAccess":
            self._perform_protected_operation()
        else:
            raise PermissionError("Access Denied")

    def _perform_protected_operation(self):
        print("Performing protected operation")

# The alternate interface allows bypassing the protected access mechanism
controller = HardwareController()
print(controller.alternate_interface)  # Can be used to bypass access control

Explanation:

• Issue: The alternate_interface is publicly accessible and does not have the same protection as _primary_interface, allowing unauthorized access.
• Vulnerability: An attacker can exploit the alternate_interface to bypass the access control checks in access_hardware.

How to fix Missing Protection Mechanism for Alternate Hardware Interface?

To fix this issue, ensure that all hardware interfaces, including alternate paths, are strictly protected by the same access control mechanisms. This can be achieved by:

1. Making alternate interfaces private or protected and ensuring they adhere to the same security checks as the primary interface.
2. Implementing access control checks consistently across all interfaces.
3. Using encapsulation to prevent unauthorized access to sensitive components.

Fixed Code Example

class HardwareController:
    def __init__(self):
        self._primary_interface = "ProtectedAccess"
        self._alternate_interface = "RestrictedAccess"  # Made private and renamed for clarity
    
    def access_hardware(self, interface="primary"):
        # Unified access control for both interfaces
        if interface == "primary" and self._primary_interface == "ProtectedAccess":
            self._perform_protected_operation()
        elif interface == "alternate":
            raise PermissionError("Alternate interface access is restricted")  # Access is now consistently protected
        else:
            raise PermissionError("Access Denied")

    def _perform_protected_operation(self):
        print("Performing protected operation")

# Fixed: No direct access to alternate interface and protection applied
controller = HardwareController()
try:
    controller.access_hardware("alternate")  # Attempt to access alternate interface
except PermissionError as e:
    print(e)  # Output: Alternate interface access is restricted

Explanation:

• Fix: The alternate_interface is now private (_alternate_interface) and cannot be accessed directly from outside the class.
• Unified Access Control: The access_hardware method now applies consistent security checks to both the primary and alternate interfaces, preventing unauthorized access through the alternate path.
• Encapsulation: The use of encapsulation ensures that all access control logic is managed internally within the class, reducing the risk of bypassing security mechanisms.