CWE-570 Base Borrador

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.

Definición

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.
Impacto en el mundo real

Real-world CVEs caused by CWE-570

Todavía no hay CVEs públicos enlazados a esta CWE en el catálogo de MITRE.

Cómo lo explotan los atacantes

Ruta del atacante paso a paso

  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.

Ejemplo de código vulnerable

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);
  		}
  }
Ejemplo de código seguro

Secure Java

This can be easily corrected by updating the appropriate variable.

Seguro 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.
Lista de prevención

How to prevent CWE-570

  • Testing Use Static Analysis tools to spot such conditions.
Señales de detección

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.)

Auto-corrección de Plexicus

Plexicus detecta automáticamente CWE-570 y abre un PR de corrección en menos de 60 segundos.

Codex Remedium escanea cada commit, identifica esta debilidad concreta y entrega un pull request listo para revisión con el parche. Sin tickets. Sin traspasos.

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Preguntas frecuentes

Frequently asked questions

¿Qué es 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.

¿Qué gravedad tiene CWE-570?

MITRE no ha publicado una calificación de probabilidad de explotación para esta debilidad. Trátala como de impacto medio hasta que tu modelo de amenazas demuestre lo contrario.

¿Qué lenguajes o plataformas se ven afectados por CWE-570?

MITRE no ha especificado plataformas afectadas para esta CWE — puede aplicar a la mayoría de los stacks de aplicaciones.

¿Cómo puedo prevenir CWE-570?

Use Static Analysis tools to spot such conditions.

¿Cómo detecta y corrige Plexicus CWE-570?

El motor SAST de Plexicus detecta la firma de flujo de datos para CWE-570 en cada commit. Cuando hay coincidencia, nuestro agente Codex Remedium abre un PR de corrección con el código corregido, las pruebas y un resumen de una línea para el revisor.

¿Dónde puedo aprender más sobre CWE-570?

MITRE publica la definición canónica en https://cwe.mitre.org/data/definitions/570.html. También puedes consultar la documentación de OWASP y NIST para guías relacionadas.

Debilidades relacionadas

Weaknesses related to CWE-570

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CWE-1061 Hermano

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CWE-1066 Hermano

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CWE-1068 Hermano

Inconsistency Between Implementation and Documented Design

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Recursos

Further reading

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