CWE-1037: Processor Optimization Removal or Modification of Security-critical Code

What is Processor Optimization Removal or Modification of Security-critical Code?

• Overview: This vulnerability occurs when processor optimizations remove or alter security-critical code that developers have implemented, potentially weakening the intended security protections without the developer's knowledge.

• Exploitation Methods:

• Attackers can exploit this vulnerability by targeting optimized code that omits security checks.
• Common attack patterns include analyzing software behavior to identify missing security mechanisms and leveraging these gaps for unauthorized access or data manipulation.

• Security Impact:

• Direct consequences include bypassing authentication mechanisms, data integrity checks, or other security controls.
• Potential cascading effects include system compromise, data breaches, and unauthorized resource access.
• Business impact may encompass financial loss, reputational damage, and compliance violations.

• Prevention Guidelines:

• Specific code-level fixes include explicitly marking critical code sections to prevent optimization or using volatile or no-optimize pragmas where available.
• Security best practices involve conducting thorough code reviews and static analysis to ensure critical code paths are preserved.
• Recommended tools and frameworks include using compiler settings that minimize aggressive optimization and employing automated testing to detect unexpected changes in security behavior.

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Technical Details

Likelihood of Exploit: Low

Affected Languages: Not Language-Specific

Affected Technologies: Processor Hardware

Vulnerable Code Example

def security_critical_operation(user_input):
    # The following security check is intended to prevent execution if the input is dangerous
    if user_input == "dangerous_operation":
        return "Operation not allowed"
    
    # Vulnerable code: The security check might be removed by aggressive optimization
    # since it doesn't seem to affect the program logic
    execute_operation(user_input)
    
def execute_operation(operation):
    print(f"Executing {operation}")

Explanation

The security check in the above code is vulnerable to being optimized away because it doesn't directly affect the program's state or output when the condition is false. Some interpreters might optimize out such checks if they determine that they don't impact the program's logic, especially in complex or minified code scenarios. In this example, the security check returns a string, but it doesn't alter the program's control flow or state in a way that would prevent potentially dangerous operations from executing.

How to fix Processor Optimization Removal or Modification of Security-critical Code?

To prevent processor optimization from removing security-critical checks, ensure that the checks have a clear impact on the program's state or output in a way that optimizers recognize. One way to achieve this is by structuring the code so that the result of the security check is directly used in control flow that affects visible program behavior.

Best Practices:

• Use explicit control flow changes (like raising exceptions) that impact the program's output or state.
• Avoid patterns that can be perceived as no-ops, like conditional returns with no variable changes.
• Ensure that security checks have side effects that cannot be optimized away.

Fixed Code Example

def security_critical_operation(user_input):
    # The following security check now affects the program flow directly by raising an exception
    if user_input == "dangerous_operation":
        raise ValueError("Operation not allowed")
    
    # Fixed code: The security check now directly affects program flow, preventing it from being optimized away
    execute_operation(user_input)
    
def execute_operation(operation):
    print(f"Executing {operation}")

Explanation

• The security check now raises an exception if the condition is met. This change ensures that the check has a visible effect on the program's execution flow, preventing optimizers from removing it.
• By affecting the control flow with an exception, we make sure that the security mechanism remains intact and functional regardless of any optimization that may occur. This approach ensures that dangerous operations are effectively blocked, maintaining the integrity and security of the application.