CWE-763 Base Incompleto

Release of Invalid Pointer or Reference

This vulnerability occurs when a program tries to free a memory resource back to the system but uses an incorrect deallocation method or calls the correct method improperly.

Definição

What is CWE-763?

This vulnerability occurs when a program tries to free a memory resource back to the system but uses an incorrect deallocation method or calls the correct method improperly.
This issue typically arises from mismatched memory management functions. For example, memory allocated with one function (like `malloc`) is incorrectly freed using a non-compatible function from a different API (like `delete`), leading to heap corruption and instability. This mismatch, often called CWE-762, breaks the underlying memory manager's expectations. Even when using the correct function pair, developers can misuse them. A common mistake is calling the deallocation function with an invalid pointer—such as one that was already freed, points to stack memory, or was never allocated. This scenario, related to CWE-761, causes crashes or undefined behavior because the system cannot process the flawed release request.
Impacto no mundo real

Real-world CVEs caused by CWE-763

  • CVE-2019-11930

    function "internally calls 'calloc' and returns a pointer at an index... inside the allocated buffer. This led to freeing invalid memory."

Como os atacantes a exploram

Trajeto do atacante passo a passo

  1. 1

    This code attempts to tokenize a string and place it into an array using the strsep function, which inserts a \0 byte in place of whitespace or a tab character. After finishing the loop, each string in the AP array points to a location within the input string.

  2. 2

    Since strsep is not allocating any new memory, freeing an element in the middle of the array is equivalent to free a pointer in the middle of inputstring.

  3. 3

    This example allocates a BarObj object using the new operator in C++, however, the programmer then deallocates the object using free(), which may lead to unexpected behavior.

  4. 4

    Instead, the programmer should have either created the object with one of the malloc family functions, or else deleted the object with the delete operator.

  5. 5

    In this example, the programmer dynamically allocates a buffer to hold a string and then searches for a specific character. After completing the search, the programmer attempts to release the allocated memory and return SUCCESS or FAILURE to the caller. Note: for simplification, this example uses a hard-coded "Search Me!" string and a constant string length of 20.

Exemplo de código vulnerável

Vulnerable C

This code attempts to tokenize a string and place it into an array using the strsep function, which inserts a \0 byte in place of whitespace or a tab character. After finishing the loop, each string in the AP array points to a location within the input string.

Vulnerável C 
char **ap, *argv[10], *inputstring;
  for (ap = argv; (*ap = strsep(&inputstring, " \t")) != NULL;)
  		if (**ap != '\0')
  			if (++ap >= &argv[10])
  				break;
  /.../
  free(ap[4]);
Exemplo de código seguro

Secure C++

Instead, the programmer should have either created the object with one of the malloc family functions, or else deleted the object with the delete operator.

Seguro C++ 
void foo(){
  		BarObj *ptr = new BarObj()
```
/* do some work with ptr here */* 
  		
  		...
  		
  		delete ptr;}
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-763

  • Implementation Only call matching memory management functions. Do not mix and match routines. For example, when you allocate a buffer with malloc(), dispose of the original pointer with free().
  • Implementation When programming in C++, consider using smart pointers provided by the boost library to help correctly and consistently manage memory.
  • Architecture and Design Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. For example, glibc in Linux provides protection against free of invalid pointers.
  • Architecture and Design Use a language that provides abstractions for memory allocation and deallocation.
  • Testing Use a tool that dynamically detects memory management problems, such as valgrind.
Sinais de deteção

How to detect CWE-763

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-763 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-763?

This vulnerability occurs when a program tries to free a memory resource back to the system but uses an incorrect deallocation method or calls the correct method improperly.

Qual a gravidade do CWE-763?

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-763?

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

Como posso prevenir o CWE-763?

Only call matching memory management functions. Do not mix and match routines. For example, when you allocate a buffer with malloc(), dispose of the original pointer with free(). When programming in C++, consider using smart pointers provided by the boost library to help correctly and consistently manage memory.

Como é que o Plexicus deteta e corrige o CWE-763?

O motor SAST do Plexicus correlaciona a assinatura de fluxo de dados do CWE-763 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-763?

A MITRE publica a definição canónica em https://cwe.mitre.org/data/definitions/763.html. Pode também consultar a documentação da OWASP e do NIST para orientações adjacentes.

Fraquezas relacionadas

Weaknesses related to CWE-763

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CWE-761 Irmão

Free of Pointer not at Start of Buffer

This vulnerability occurs when a program incorrectly frees a memory pointer that no longer points to the beginning of the allocated heap…

CWE-762 Irmão

Mismatched Memory Management Routines

This vulnerability occurs when a program uses incompatible functions to allocate and free memory. For example, freeing memory with a…

CWE-772 Irmão

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CWE-775 Irmão

Missing Release of File Descriptor or Handle after Effective Lifetime

This vulnerability occurs when a program fails to properly close file descriptors or handles after they are no longer needed, leaving…

Recursos

Further reading

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