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.
CWE-469 Base Borrador
Use of Pointer Subtraction to Determine Size
This vulnerability occurs when a program calculates a size or offset by subtracting two memory pointers, but the pointers point to locations in different memory blocks, leading to an incorrect and…
Definición
What is CWE-469?
This vulnerability occurs when a program calculates a size or offset by subtracting two memory pointers, but the pointers point to locations in different memory blocks, leading to an incorrect and potentially dangerous result.
Pointer subtraction is a valid C/C++ operation, but it only yields a meaningful size or element count when both pointers point within the same contiguous memory allocation (like a single array or buffer). When developers use this trick on pointers from different allocations, the calculation produces a nonsensical value based on the arbitrary memory distance between the two chunks. This flawed size is then often used in buffer operations, leading to out-of-bounds reads or writes, memory corruption, and crashes.
Detecting these flaws manually is tricky because the code looks mathematically simple. While SAST tools can flag the pattern, Plexicus uses AI to analyze the pointer origins and suggest the correct fix—such as storing the allocation size separately—saving hours of debugging. Managing this at scale across a large codebase is difficult; an ASPM like Plexicus can help you track and remediate these subtle memory flaws across your entire application stack.
Impacto en el mundo real
Real-world CVEs caused by CWE-469
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
Identifica una ruta de código que maneje entrada no confiable sin validación.
- 2
Crea un payload que ejercite el comportamiento inseguro — inyección, traversal, overflow o abuso de lógica.
- 3
Envía el payload a través de una solicitud normal y observa la reacción de la aplicación.
- 4
Itera hasta que la respuesta filtre datos, ejecute código del atacante o escale privilegios.
Ejemplo de código vulnerable
Vulnerable C
The following example contains the method size that is used to determine the number of nodes in a linked list. The method is passed a pointer to the head of the linked list.
struct node {
int data;
struct node* next;
};
```
// Returns the number of nodes in a linked list from*
*// the given pointer to the head of the list.*
int size(struct node* head) {
```
struct node* current = head;
struct node* tail;
while (current != NULL) {
tail = current;
current = current->next;
}
return tail - head;
}
```
// other methods for manipulating the list*
... Ejemplo de código seguro
Secure C
However, the method creates a pointer that points to the end of the list and uses pointer subtraction to determine the number of nodes in the list by subtracting the tail pointer from the head pointer. There no guarantee that the pointers exist in the same memory area, therefore using pointer subtraction in this way could return incorrect results and allow other unintended behavior. In this example a counter should be used to determine the number of nodes in the list, as shown in the following code.
...
int size(struct node* head) {
struct node* current = head;
int count = 0;
while (current != NULL) {
count++;
current = current->next;
}
return count;
} 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-469
- Implementation Save an index variable. This is the recommended solution. Rather than subtract pointers from one another, use an index variable of the same size as the pointers in question. Use this variable to "walk" from one pointer to the other and calculate the difference. Always validate this number.
Señales de detección
How to detect CWE-469
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.)
Plexicus detecta automáticamente CWE-469 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.
Preguntas frecuentes ¿Qué es CWE-469?
¿Qué gravedad tiene CWE-469?
¿Qué lenguajes o plataformas se ven afectados por CWE-469?
¿Cómo puedo prevenir CWE-469?
¿Cómo detecta y corrige Plexicus CWE-469?
¿Dónde puedo aprender más sobre CWE-469?
Frequently asked questions
¿Qué es CWE-469?
This vulnerability occurs when a program calculates a size or offset by subtracting two memory pointers, but the pointers point to locations in different memory blocks, leading to an incorrect and potentially dangerous result.
¿Qué gravedad tiene CWE-469?
MITRE califica la probabilidad de explotación como Media — la explotación es realista pero suele requerir condiciones específicas.
¿Qué lenguajes o plataformas se ven afectados por CWE-469?
MITRE lists the following affected platforms: C, C++.
¿Cómo puedo prevenir CWE-469?
Save an index variable. This is the recommended solution. Rather than subtract pointers from one another, use an index variable of the same size as the pointers in question. Use this variable to "walk" from one pointer to the other and calculate the difference. Always validate this number.
¿Cómo detecta y corrige Plexicus CWE-469?
El motor SAST de Plexicus detecta la firma de flujo de datos para CWE-469 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-469?
MITRE publica la definición canónica en https://cwe.mitre.org/data/definitions/469.html. También puedes consultar la documentación de OWASP y NIST para guías relacionadas.
Debilidades relacionadas
Weaknesses related to CWE-469
CWE-682 Padre
Incorrect Calculation
This vulnerability occurs when software performs a calculation that produces wrong or unexpected results, which are then used to make…
CWE-128 Hermano
Wrap-around Error
A wrap-around error happens when a variable exceeds the maximum value its data type can hold, causing it to unexpectedly reset to a very…
CWE-131 Hermano
Incorrect Calculation of Buffer Size
This vulnerability occurs when a program miscalculates the amount of memory needed for a buffer, potentially leading to a buffer overflow…
CWE-1335 Hermano
Incorrect Bitwise Shift of Integer
This vulnerability occurs when a program attempts to shift an integer's bits by an invalid amount—either a negative number or a value…
CWE-1339 Hermano
Insufficient Precision or Accuracy of a Real Number
This vulnerability occurs when a program uses a data type or algorithm that cannot accurately represent or calculate the fractional part…
CWE-135 Hermano
Incorrect Calculation of Multi-Byte String Length
This vulnerability occurs when software incorrectly measures the length of strings containing multi-byte or wide characters, leading to…
CWE-190 Hermano
Integer Overflow or Wraparound
Integer overflow or wraparound occurs when a calculation produces a numeric result that exceeds the maximum value a variable can hold.…
CWE-191 Hermano
Integer Underflow (Wrap or Wraparound)
Integer underflow occurs when a subtraction operation results in a value smaller than the data type's minimum limit, causing the value to…
CWE-193 Hermano
Off-by-one Error
An off-by-one error occurs when a program incorrectly calculates a boundary, such as a loop counter or array index, by being one unit too…
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