CWE-1262: Improper Access Control for Register Interface

What is Improper Access Control for Register Interface?

• Overview: Improper Access Control for Register Interface (CWE-1262) occurs when a product uses memory-mapped I/O registers to interface with hardware, but fails to properly control access to these registers. This could allow unauthorized software to manipulate hardware settings.

• Exploitation Methods:

• Attackers can exploit this vulnerability by crafting malicious software that accesses and modifies security-critical hardware data through poorly secured register interfaces.
• Common attack patterns include unauthorized reading or writing to hardware registers, exploiting lack of authentication or permission checks, and injecting malicious code to alter hardware behavior.

• Security Impact:

• Direct consequences of successful exploitation include unauthorized modification of hardware settings and potential exposure of sensitive data.
• Potential cascading effects include system instability, data corruption, or enabling further attacks on other system components.
• Business impact might involve loss of customer trust, legal liabilities, and financial loss due to data breaches or downtime.

• Prevention Guidelines:

• Implement strict access controls and permissions for memory-mapped I/O registers, ensuring only authorized software can interact with them.
• Follow security best practices, such as least privilege principle, input validation, and regular security audits of hardware interfaces.
• Use recommended tools and frameworks that enforce secure coding practices for handling hardware interfaces, and consider using hardware-assisted security features to protect critical registers.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Not Language-Specific

Affected Technologies: Not Technology-Specific

Vulnerable Code Example

# device_control.py {12-15}
class DeviceRegisterInterface:
    def __init__(self):
        # Memory-mapped registers
        self.registers = [0] * 256

    def write_register(self, index, value):
        # Directly access hardware registers without any access control
        self.registers[index] = value

    def read_register(self, index):
        # Directly access hardware registers without any access control
        return self.registers[index]

# Usage
device = DeviceRegisterInterface()
device.write_register(128, 255)  # Writing to register
value = device.read_register(128)  # Reading from register

Explanation:

• Direct Access: The code above allows direct access to memory-mapped hardware registers without any form of access control. This poses a significant security risk as any part of the program with access to this class can modify or read the registers, potentially leading to unauthorized manipulation or access to sensitive hardware functionality.

How to fix Improper Access Control for Register Interface?

To address this vulnerability, implement an access control mechanism to ensure that only authorized users or components can read or write to specific registers. Role-Based Access Control (RBAC) or similar strategies can be used to enforce permissions. Additionally, logging register access can help in tracking changes and detecting unauthorized access attempts.

Fixed Code Example

# device_control.py {12-23}
class DeviceRegisterInterface:
    def __init__(self):
        self.registers = [0] * 256
        # Define access control for roles
        self.authorized_roles = {
            'admin': range(0, 256),  # Admin can access all registers
            'user': range(0, 128)    # Regular user can access first half of the registers
        }

    def _check_access(self, role, index):
        # Check if the role is authorized to access the specific register
        if index not in self.authorized_roles.get(role, []):
            raise PermissionError(f"Access denied for role {role} to register {index}")

    def write_register(self, role, index, value):
        self._check_access(role, index)
        self.registers[index] = value

    def read_register(self, role, index):
        self._check_access(role, index)
        return self.registers[index]

# Usage
device = DeviceRegisterInterface()
try:
    device.write_register('admin', 128, 255)  # Admin has access
    value = device.read_register('admin', 128)
    print("Register value:", value)
except PermissionError as e:
    print(e)

try:
    device.write_register('user', 200, 100)  # User does not have access
except PermissionError as e:
    print(e)

Explanation:

• Access Control Check: Introduced a private method _check_access that verifies if the provided role has permission to access a specific register, ensuring unauthorized access is blocked.
• Role-Based Access Control (RBAC): Defined authorized_roles to specify which roles can access which registers, providing a clear and secure access policy.
• Exception Handling: Added exception handling to manage unauthorized access attempts, raising a PermissionError if access is denied, which is caught and handled gracefully.

This implementation effectively ensures that only authorized roles can perform read/write operations on the registers, thereby mitigating the risk of unauthorized access to hardware functionality.