CWE-1253: Incorrect Selection of Fuse Values

What is Incorrect Selection of Fuse Values?

• Overview: Incorrect Selection of Fuse Values (CWE-1253) is a vulnerability where the security of a system relies on fuses being unblown to maintain a secure state. If fuses are blown, an attacker can change the system to an insecure state.

• Exploitation Methods:

• Attackers can exploit this vulnerability by physically blowing the fuses, which may be possible through direct access to the hardware.
• Common attack patterns include manipulating fuse states to bypass security configurations and gain unauthorized access.

• Security Impact:

• Direct consequences of successful exploitation include system compromise and unauthorized access to sensitive data or operations.
• Potential cascading effects may involve further exploitation of system vulnerabilities or exposure of additional security weaknesses.
• Business impact can be severe, including data breaches, loss of customer trust, and potential financial penalties.

• Prevention Guidelines:

• Specific code-level fixes include ensuring that security logic does not rely solely on fuse states and incorporating additional security checks.
• Security best practices involve using multi-layered security approaches and avoiding negative logic reliance for critical security states.
• Recommended tools and frameworks include using hardware security modules (HSMs) and implementing tamper-resistant designs in hardware.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Not Language-Specific

Affected Technologies: Not Technology-Specific

Vulnerable Code Example

class SystemSecurity:
    def __init__(self):
        # Using a simple flag to denote secure state based on fuse status
        # If fuse is intact (False), the system is secure; if blown (True), it is not
        self.fuse_blown = False
    
    def check_system_security(self):
        # Security logic is inverted; the system should be secure when the fuse is unblown
        if self.fuse_blown:
            return "System is insecure!"
        return "System is secure!"

Explanation:

• Vulnerability: The security of the system relies solely on a single boolean flag, fuse_blown. This makes the system vulnerable because an attacker could easily manipulate this flag to alter the security state. The logic incorrectly assumes that if the fuse is blown (fuse_blown = True), the system is insecure, which is a simplistic and unreliable security measure.

How to fix Incorrect Selection of Fuse Values?

To address this issue, the security state should incorporate multiple checks and not depend solely on a single flag. This creates a more robust and secure system that is less susceptible to being compromised by a single point of failure.

Best Practices:

1. Redundant Checks: Implement multiple checks to ensure the system's secure state is not reliant on a single point of failure.
2. Use Secure Defaults: The default state of the system should be secure, with deviations requiring strict validation.
3. Validation and Monitoring: Regularly validate system security states and monitor for unauthorized changes.

Fixed Code Example

class SystemSecurity:
    def __init__(self):
        # Default secure state, independent of fuse state directly
        self.fuse_blown = False
        self.secure_mode_enabled = True  # Adding an additional security measure

    def validate_security(self):
        # Additional security logic to ensure comprehensive checks
        return not self.fuse_blown and self.secure_mode_enabled

    def check_system_security(self):
        # Corrected logic to ensure system security is robust
        if not self.validate_security():
            return "System is insecure!"
        return "System is secure!"

Explanation:

• Fix Implementation: Introduced a secure_mode_enabled flag that defaults to True, adding an additional layer of security. The validate_security method checks both fuse_blown and secure_mode_enabled to ensure a comprehensive security assessment. This approach mitigates the risk of a single point of failure.
• Robust Security Logic: The check_system_security method now utilizes validate_security, which combines multiple conditions to determine the security status, thereby enhancing the system's resilience against attacks.