CWE-570 Base Draft

Expression is Always False

This vulnerability occurs when code contains a conditional expression that can never evaluate to true, causing a section of the program to be permanently unreachable.

Definition

What is CWE-570?

This vulnerability occurs when code contains a conditional expression that can never evaluate to true, causing a section of the program to be permanently unreachable.
An 'always false' expression is a type of dead code that often results from logical errors, incorrect assumptions about data, or leftover debugging checks. For example, comparing a variable against a fixed value it can never hold, or checking a condition after it has already been definitively ruled out earlier in the logic. This creates a maintenance hazard, as developers might waste time debugging non-functional code, and it can mask deeper logical flaws that affect the program's real behavior. While the unreachable code itself might not directly cause a crash, it indicates flawed reasoning that could lead to security issues elsewhere. It can prevent security-critical validation routines from executing, cause resource leaks if cleanup code is skipped, or create unexpected program flow that attackers could analyze to understand the codebase. Regular code reviews and static analysis tools are effective at catching these expressions before they reach production.
Real-world impact

Real-world CVEs caused by CWE-570

No public CVE references are linked to this CWE in MITRE's catalog yet.

How attackers exploit it

Step-by-step attacker path

  1. 1

    In the following Java example the updateUserAccountOrder() method used within an e-business product ordering/inventory application will validate the product number that was ordered and the user account number. If they are valid, the method will update the product inventory, the user account, and the user order appropriately.

  2. 2

    However, the method never sets the isValidAccount variable after initializing it to false so the isValidProduct is mistakenly used twice. The result is that the expression "isValidProduct && isValidAccount" will always evaluate to false, so the updateAccountOrder() method will never be invoked. This will create serious problems with the product ordering application since the user account and inventory databases will be updated but the order will not be updated.

  3. 3

    This can be easily corrected by updating the appropriate variable.

  4. 4

    In the following example, the hasReadWriteAccess method uses bit masks and bit operators to determine if a user has read and write privileges for a particular process. The variable mask is defined as a bit mask from the BIT_READ and BIT_WRITE constants that have been defined. The variable mask is used within the predicate of the hasReadWriteAccess method to determine if the userMask input parameter has the read and write bits set.

  5. 5

    However the bit operator used to initialize the mask variable is the AND operator rather than the intended OR operator (CWE-480), this resulted in the variable mask being set to 0. As a result, the if statement will always evaluate to false and never get executed.

Vulnerable code example

Vulnerable Java

In the following Java example the updateUserAccountOrder() method used within an e-business product ordering/inventory application will validate the product number that was ordered and the user account number. If they are valid, the method will update the product inventory, the user account, and the user order appropriately.

Vulnerable Java 
public void updateUserAccountOrder(String productNumber, String accountNumber) {
  		boolean isValidProduct = false;
  		boolean isValidAccount = false;
  		if (validProductNumber(productNumber)) {
  			isValidProduct = true;
  			updateInventory(productNumber);
  		}
  		else {
  			return;
  		}
  		if (validAccountNumber(accountNumber)) {
  			isValidProduct = true;
  			updateAccount(accountNumber, productNumber);
  		}
  		if (isValidProduct && isValidAccount) {
  			updateAccountOrder(accountNumber, productNumber);
  		}
  }
Secure code example

Secure Java

This can be easily corrected by updating the appropriate variable.

Secure Java 
...
  if (validAccountNumber(accountNumber)) {
  	isValidAccount = true;
  	updateAccount(accountNumber, productNumber);
  }
  ...
What changed: the unsafe sink is replaced (or the input is validated/escaped) so the same payload no longer triggers the weakness.
Prevention checklist

How to prevent CWE-570

  • Testing Use Static Analysis tools to spot such conditions.
Detection signals

How to detect CWE-570

Automated Static Analysis High

Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)

Plexicus auto-fix

Plexicus auto-detects CWE-570 and opens a fix PR in under 60 seconds.

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Frequently asked questions

Frequently asked questions

What is CWE-570?

This vulnerability occurs when code contains a conditional expression that can never evaluate to true, causing a section of the program to be permanently unreachable.

How serious is CWE-570?

MITRE has not published a likelihood-of-exploit rating for this weakness. Treat it as medium-impact until your threat model proves otherwise.

What languages or platforms are affected by CWE-570?

MITRE has not specified affected platforms for this CWE — it can apply across most application stacks.

How can I prevent CWE-570?

Use Static Analysis tools to spot such conditions.

How does Plexicus detect and fix CWE-570?

Plexicus's SAST engine matches the data-flow signature for CWE-570 on every commit. When a match is found, our Codex Remedium agent opens a fix PR with the corrected code, tests, and a one-line summary for the reviewer.

Where can I learn more about CWE-570?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/570.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-570

CWE-710 Parent

Improper Adherence to Coding Standards

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CWE-1041 Sibling

Use of Redundant Code

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CWE-1044 Sibling

Architecture with Number of Horizontal Layers Outside of Expected Range

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CWE-1048 Sibling

Invokable Control Element with Large Number of Outward Calls

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CWE-1059 Sibling

Insufficient Technical Documentation

This weakness occurs when a software or hardware product lacks comprehensive technical documentation. Missing or incomplete details about…

CWE-1061 Sibling

Insufficient Encapsulation

This weakness occurs when a software component exposes too much of its internal workings, such as data structures or implementation logic.…

CWE-1065 Sibling

Runtime Resource Management Control Element in a Component Built to Run on Application Servers

This weakness occurs when an application built to run on a managed application server bypasses the server's high-level APIs and instead…

CWE-1066 Sibling

Missing Serialization Control Element

This weakness occurs when a class or data structure is marked as serializable but lacks the required control methods to properly handle…

CWE-1068 Sibling

Inconsistency Between Implementation and Documented Design

This weakness occurs when the actual code implementation deviates from the intended design described in its official documentation,…

Resources

Further reading

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