What is Expression is Always False (CWE-570)?

TL;DR: Expression is Always False (CWE-570) is a software quality degradation issue where an expression evaluates to false regardless of program state, leading to inefficient execution. Refactoring and simplifying logic can resolve this.

What is Expression is Always False?

Expression is Always False (CWE-570) is a type of software quality degradation issue where an expression evaluates to false regardless of the program’s state. As defined by the MITRE Corporation under CWE-570, and classified by the OWASP Foundation as not directly mapped.

Quick Summary

Expression is Always False impacts software maintainability and performance by introducing unnecessary code that does not contribute to functionality or logic flow. Jump to: Overview · Business Impact · Attack Scenario · Detection · Fixing · Framework Fixes · AI Prompt · Best Practices · FAQ · Related Vulnerabilities · References

Jump to: Quick Summary · Expression is Always False Overview · How Expression is Always False Works · Business Impact of Expression is Always False · Expression is Always False Attack Scenario · How to Detect Expression is Always False · How to Fix Expression is Always False · Framework-Specific Fixes for Expression is Always False · How to Ask AI to Check Your Code for Expression is Always False · Expression is Always False Best Practices Checklist · Expression is Always False FAQ · Vulnerabilities Related to Expression is Always False · References · Scan Your Own Site

Expression is Always False Overview

What: An expression in the program evaluates to false under all possible conditions.

Why it matters: This can lead to inefficient code execution and maintenance issues, as such expressions do not contribute to the logic flow or functionality of the software.

Where it occurs: In any programming language where conditional logic is present.

Who is affected: Developers who write or maintain code with unnecessary checks.

Who is NOT affected: Systems that have robust refactoring practices in place and eliminate dead code.

How Expression is Always False Works

Root Cause

The root cause of this issue lies in the presence of an expression that evaluates to false under all conditions, leading to unnecessary code execution.

Attack Flow

1. An expression is written with a condition that will never be true.
2. The program executes but does not change state due to the always-false expression.
3. Maintenance issues arise as developers may overlook or misinterpret such expressions.

Prerequisites to Exploit

• The existence of an expression that evaluates to false under all conditions.
• No refactoring or dead code removal practices in place.

Vulnerable Code

if False:
    print("This will never execute.")

Explanation: This snippet demonstrates a condition that is always false, leading to unnecessary code execution and potential maintenance issues.

Secure Code

# Remove the unnecessary conditional check.
print("This executes as intended.")

Explanation: The secure version removes the dead code by eliminating the unnecessary conditional check.

Business Impact of Expression is Always False

• Confidentiality: None directly impacted, but poor quality can indirectly affect security through maintenance issues.
• Integrity: Code integrity may be compromised due to unnecessary logic that could lead to misinterpretation or bugs.
• Availability: Performance degradation due to unnecessary CPU cycles spent on evaluating expressions.

Expression is Always False Attack Scenario

1. A developer writes an expression that evaluates to false under all conditions.
2. The program executes but does not change state due to the always-false condition.
3. Maintenance issues arise as developers may overlook or misinterpret such expressions, leading to potential bugs and inefficiencies.

How to Detect Expression is Always False

Manual Testing

• Review conditional logic for expressions that evaluate to false under all conditions.
• Check if dead code removal practices are in place.
• Ensure refactoring processes eliminate unnecessary checks.

Automated Scanners (SAST / DAST)

Static analysis tools can identify expressions that will never evaluate to true or false. Dynamic testing may not be necessary for this issue, but it helps ensure no runtime conditions change the evaluation of such expressions.

PenScan Detection

PenScan’s scanner engines like ZAP and Nuclei can detect unnecessary conditional checks in code.

False Positive Guidance

A real finding will show an expression that evaluates to false under all conditions. A false positive may occur if a condition is contextually valid but appears always false out of context.

How to Fix Expression is Always False

• Refactor the code by simplifying or removing unnecessary conditional checks.
• Ensure dead code removal practices are in place and regularly applied.
• Review refactoring processes to eliminate redundant logic.

Framework-Specific Fixes for Expression is Always False

Python/Django

# Remove unnecessary condition.
print("This executes as intended.")

Explanation: The secure version removes the dead code by eliminating the unnecessary conditional check.

How to Ask AI to Check Your Code for Expression is Always False

Expression is Always False Best Practices Checklist

✅ Review conditional logic for expressions that evaluate to false under all conditions.

✅ Ensure dead code removal practices are in place and regularly applied.

✅ Refactor the code by simplifying or removing unnecessary checks.

✅ Check if refactoring processes eliminate redundant logic.

✅ Validate refactored code through unit tests and manual reviews.

Expression is Always False FAQ

How does an expression that always evaluates to false affect software quality?

It can lead to unexpected behavior, poor performance, and maintenance issues due to unnecessary code execution.

Can Expression is Always False be detected through automated testing tools?

Yes, static analysis tools can identify expressions that will never evaluate to true or false.

What are the common reasons for an expression being always false in a program?

Common reasons include logical errors, incorrect assumptions about variable states, and misinterpreted conditions.

How does Expression is Always False impact system performance?

It can cause unnecessary CPU cycles to be spent on evaluating expressions that have no effect.

What are the best practices for preventing Expression is Always False in code reviews?

Review and simplify conditional logic, ensuring all conditions can realistically occur during program execution.

Can dead code removal tools help identify Expression is Always False issues?

Yes, such tools can detect unused or unreachable code that includes expressions with no impact.

Vulnerabilities Related to Expression is Always False

References

• MITRE - CWE-570
• NVD - NIST

Scan Your Own Site

Manual code review catches what you know to look for. An automated scan catches what you didn’t. Scan your own website using PenScan to find Expression is Always False and other risks before an attacker does.