CWE-704 Classe Incompleto

Incorrect Type Conversion or Cast

This vulnerability occurs when software incorrectly changes data from one type to another, leading to unexpected behavior or security flaws.

Definição

What is CWE-704?

This vulnerability occurs when software incorrectly changes data from one type to another, leading to unexpected behavior or security flaws.
Incorrect type conversion, often called a type confusion or type casting bug, happens when a developer assumes a piece of data is one kind of object or structure (like an integer, string, or class instance) but the program treats it as another. This mismatch can cause the application to misinterpret the data's meaning, access the wrong memory locations, or call incorrect functions, which attackers can exploit to crash the system, leak information, or execute arbitrary code. These issues are common in languages that allow manual type casting (like C/C++) or have weak typing, but they can also appear in higher-level languages during serialization, inter-process communication, or when using reflection. To prevent this, developers should validate data types before conversion, use safe casting functions provided by the language, and implement strict input validation at all system boundaries.
Impacto no mundo real

Real-world CVEs caused by CWE-704

  • CVE-2021-43537

    Chain: in a web browser, an unsigned 64-bit integer is forcibly cast to a 32-bit integer (CWE-681) and potentially leading to an integer overflow (CWE-190). If an integer overflow occurs, this can cause heap memory corruption (CWE-122)

  • CVE-2022-3979

    Chain: data visualization program written in PHP uses the "!=" operator instead of the type-strict "!==" operator (CWE-480) when validating hash values, potentially leading to an incorrect type conversion (CWE-704)

Como os atacantes a exploram

Trajeto do atacante passo a passo

  1. 1

    In this example, depending on the return value of accecssmainframe(), the variable amount can hold a negative value when it is returned. Because the function is declared to return an unsigned value, amount will be implicitly cast to an unsigned number.

  2. 2

    If the return value of accessmainframe() is -1, then the return value of readdata() will be 4,294,967,295 on a system that uses 32-bit integers.

  3. 3

    The following code uses a union to support the representation of different types of messages. It formats messages differently, depending on their type.

  4. 4

    The code intends to process the message as a NAME_TYPE, and sets the default message to "Hello World." However, since both buf.name and buf.nameID are part of the same union, they can act as aliases for the same memory location, depending on memory layout after compilation.

  5. 5

    As a result, modification of buf.nameID - an int - can effectively modify the pointer that is stored in buf.name - a string.

Exemplo de código vulnerável

Vulnerable C

In this example, depending on the return value of accecssmainframe(), the variable amount can hold a negative value when it is returned. Because the function is declared to return an unsigned value, amount will be implicitly cast to an unsigned number.

Vulnerável C 
unsigned int readdata () {
  	int amount = 0;
  	...
  	amount = accessmainframe();
  	...
  	return amount;
  }
Exemplo de código seguro

Secure pseudo

Seguro pseudo 
// Validate, sanitize, or use a safe API before reaching the sink.
function handleRequest(input) {
  const safe = validateAndEscape(input);
  return executeWithGuards(safe);
}
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-704

  • Architecture Use safe-by-default frameworks and APIs that prevent the unsafe pattern from being expressible.
  • Implementation Validate input at trust boundaries; use allowlists, not denylists.
  • Implementation Apply the principle of least privilege to credentials, file paths, and runtime permissions.
  • Testing Cover this weakness in CI: SAST rules + targeted unit tests for the data flow.
  • Operation Monitor logs for the runtime signals listed in the next section.
Sinais de deteção

How to detect CWE-704

Fuzzing High

Fuzz testing (fuzzing) is a powerful technique for generating large numbers of diverse inputs - either randomly or algorithmically - and dynamically invoking the code with those inputs. Even with random inputs, it is often capable of generating unexpected results such as crashes, memory corruption, or resource consumption. Fuzzing effectively produces repeatable test cases that clearly indicate bugs, which helps developers to diagnose the issues.

Correção automática do Plexicus

O Plexicus deteta automaticamente o CWE-704 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-704?

This vulnerability occurs when software incorrectly changes data from one type to another, leading to unexpected behavior or security flaws.

Qual a gravidade do CWE-704?

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-704?

MITRE lists the following affected platforms: C, C++.

Como posso prevenir o CWE-704?

Use safe-by-default frameworks, validate untrusted input at trust boundaries, and apply the principle of least privilege. Cover the data-flow signature in CI with SAST.

Como é que o Plexicus deteta e corrige o CWE-704?

O motor SAST do Plexicus correlaciona a assinatura de fluxo de dados do CWE-704 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-704?

A MITRE publica a definição canónica em https://cwe.mitre.org/data/definitions/704.html. Pode também consultar a documentação da OWASP e do NIST para orientações adjacentes.

Fraquezas relacionadas

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Recursos

Further reading

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