CWE-1328: Security Version Number Mutable to Older Versions

What is Security Version Number Mutable to Older Versions?

• Overview: Security Version Number Mutable to Older Versions (CWE-1328) is a vulnerability where the security version number in hardware can be changed to an older version, allowing attackers to downgrade the boot firmware to a version with known vulnerabilities.

• Exploitation Methods:

• Attackers can modify the security version number to revert the system to an older, vulnerable firmware.
• Common attack patterns include roll-back attacks, where adversaries force the system to load exploitable code by downgrading the firmware.

• Security Impact:

• Direct consequences include the system operating on insecure firmware, exposing it to known vulnerabilities.
• Potential cascading effects involve the compromise of the entire system-on-chip (SoC), leading to unauthorized access and further exploitation.
• Business impact includes potential data breaches, loss of intellectual property, and damage to brand reputation.

• Prevention Guidelines:

• Specific code-level fixes involve implementing immutable security version numbers that are stored securely.
• Security best practices include using hardware features that prevent unauthorized changes to critical security settings.
• Recommended tools and frameworks include secure boot mechanisms and verified boot processes that ensure only authorized firmware can be executed.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Not Language-Specific

Affected Technologies: Security Hardware, Not Technology-Specific

Vulnerable Code Example

Python Example

class FirmwareUpdater:
    def __init__(self):
        # Vulnerable: version number can be set to an older version, allowing rollback to insecure firmware
        self.security_version = 1.0

    def set_version(self, new_version):
        # Vulnerability: this method allows setting any version number, including older, insecure ones
        self.security_version = new_version

    def update_firmware(self, firmware):
        # Simulate firmware update
        print(f"Updating firmware to version {self.security_version}...")

Explanation

In this vulnerable example, the set_version method allows any version number to be set, including older, potentially insecure versions. This opens up the possibility of downgrading the firmware to a less secure version, which could be exploited by attackers.

How to fix Security Version Number Mutable to Older Versions?

To fix the vulnerability, we need to ensure that the security version number cannot be downgraded to an older, potentially insecure version. This can be achieved by implementing a check to only allow version upgrades. Additionally, using cryptographic signatures to verify the authenticity and integrity of the firmware before updating can further enhance security. Specifically, the following practices should be adopted:

1. Immutable Versioning: Ensure that the version number is immutable and can only be incremented.
2. Version Check: Implement logic to compare the current version with the new version, allowing updates only if the new version is greater.
3. Digital Signatures: Use cryptographic signatures to verify that the firmware update is authentic and has not been tampered with.

Fixed Code Example

import hashlib

class FirmwareUpdater:
    def __init__(self):
        # Security version is initialized and should not be downgraded
        self.security_version = 1.0

    def set_version(self, new_version):
        # Fix: only allow updating to a newer version
        if new_version > self.security_version:
            self.security_version = new_version
        else:
            raise ValueError("Cannot downgrade to an older version")

    def verify_signature(self, firmware, signature):
        # Example method to verify firmware signature
        firmware_hash = hashlib.sha256(firmware).hexdigest()
        # In practice, use a trusted public key to verify the signature
        return signature == firmware_hash

    def update_firmware(self, firmware, signature):
        # Fix: verify the firmware signature before updating
        if not self.verify_signature(firmware, signature):
            raise ValueError("Firmware verification failed")

        print(f"Updating firmware to version {self.security_version}...")

Explanation

In the fixed code, we have added a version check in the set_version method that only allows the firmware version to be updated if the new version is greater than the current version. This prevents unauthorized downgrades. Additionally, the verify_signature method simulates a simple hash-based signature check to ensure firmware integrity, although in production environments, this would involve more robust cryptographic checks using public key infrastructure. These measures collectively prevent unauthorized downgrades and ensure that firmware updates are secure and legitimate.