CWE-570 Base Rascunho

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.

Definição

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 no mundo real

Real-world CVEs caused by CWE-570

Ainda não há referências CVE públicas associadas a este CWE no catálogo da MITRE.

Como os atacantes a exploram

Trajeto do atacante passo a passo

  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.

Exemplo de código vulnerável

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.

Vulnerável 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);
  		}
  }
Exemplo 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 verificação de prevenção

How to prevent CWE-570

  • Testing Use Static Analysis tools to spot such conditions.
Sinais de deteção

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.)

Correção automática do Plexicus

O Plexicus deteta automaticamente o CWE-570 e abre um PR de correção em menos de 60 segundos.

O Codex Remedium analisa cada commit, identifica esta fraqueza exata e entrega um pull request pronto para revisão com o patch. Sem tickets. Sem transferências.

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Perguntas frequentes

Frequently asked questions

O que é o 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.

Qual a gravidade do CWE-570?

A MITRE não publicou uma classificação de probabilidade de exploração para esta fraqueza. Trate-a como impacto médio até o seu modelo de ameaças provar o contrário.

Que linguagens ou plataformas são afetadas pelo CWE-570?

A MITRE não especificou as plataformas afetadas por este CWE — pode aplicar-se à maioria das stacks de aplicações.

Como posso prevenir o CWE-570?

Use Static Analysis tools to spot such conditions.

Como é que o Plexicus deteta e corrige o CWE-570?

O motor SAST do Plexicus correlaciona a assinatura de fluxo de dados do CWE-570 em cada commit. Quando é encontrada uma correspondência, o nosso agente Codex Remedium abre um PR de correção com o código corrigido, testes e um resumo de uma linha para o revisor.

Onde posso saber mais sobre o CWE-570?

A MITRE publica a definição canónica em https://cwe.mitre.org/data/definitions/570.html. Pode também consultar a documentação da OWASP e do NIST para orientações adjacentes.

Fraquezas relacionadas

Weaknesses related to CWE-570

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Inconsistency Between Implementation and Documented Design

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Recursos

Further reading

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