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 Rascunho
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…
Definição
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 no mundo real
Real-world CVEs caused by CWE-469
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
Identificar um caminho de código que trata input não confiável sem validação.
- 2
Criar um payload que explora o comportamento inseguro — injeção, traversal, overflow ou abuso de lógica.
- 3
Entregar o payload através de um pedido normal e observar a reação da aplicação.
- 4
Iterar até que a resposta exponha dados, execute código do atacante ou escale privilégios.
Exemplo de código vulnerável
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*
... Exemplo 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 verificação de prevenção
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.
Sinais de deteção
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.)
O Plexicus deteta automaticamente o CWE-469 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.
Perguntas frequentes O que é o CWE-469?
Qual a gravidade do CWE-469?
Que linguagens ou plataformas são afetadas pelo CWE-469?
Como posso prevenir o CWE-469?
Como é que o Plexicus deteta e corrige o CWE-469?
Onde posso saber mais sobre o CWE-469?
Frequently asked questions
O que é o 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.
Qual a gravidade do CWE-469?
A MITRE classifica a probabilidade de exploração como Média — a exploração é realista mas normalmente requer condições específicas.
Que linguagens ou plataformas são afetadas pelo CWE-469?
MITRE lists the following affected platforms: C, C++.
Como posso prevenir o 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.
Como é que o Plexicus deteta e corrige o CWE-469?
O motor SAST do Plexicus correlaciona a assinatura de fluxo de dados do CWE-469 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-469?
A MITRE publica a definição canónica em https://cwe.mitre.org/data/definitions/469.html. Pode também consultar a documentação da OWASP e do NIST para orientações adjacentes.
Fraquezas relacionadas
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