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.

Definición

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 en el 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."

Cómo lo explotan los atacantes

Ruta del atacante paso a paso

  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.

Ejemplo de código vulnerable

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.

Vulnerable 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]);
Ejemplo 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 prevención

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.
Señales de detección

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.

Auto-corrección de Plexicus

Plexicus detecta automáticamente CWE-763 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-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.

¿Qué gravedad tiene CWE-763?

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-763?

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

¿Cómo puedo prevenir 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.

¿Cómo detecta y corrige Plexicus CWE-763?

El motor SAST de Plexicus detecta la firma de flujo de datos para CWE-763 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-763?

MITRE publica la definición canónica en https://cwe.mitre.org/data/definitions/763.html. También puedes consultar la documentación de OWASP y NIST para guías relacionadas.

Debilidades relacionadas

Weaknesses related to CWE-763

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CWE-299 Hermano

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CWE-401 Hermano

Missing Release of Memory after Effective Lifetime

This vulnerability occurs when a program allocates memory but fails to properly release it after it's no longer needed, causing a gradual…

CWE-459 Hermano

Incomplete Cleanup

This vulnerability occurs when an application fails to properly remove temporary files, data structures, or system resources after they…

CWE-761 Hermano

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 Hermano

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 Hermano

Missing Release of Resource after Effective Lifetime

This vulnerability occurs when a program fails to properly release a system resource—like memory, file handles, or network sockets—after…

CWE-775 Hermano

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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