CWE-468: Incorrect Pointer Scaling

What is Incorrect Pointer Scaling?

• Overview: Incorrect Pointer Scaling, under CWE-468, occurs in C and C++ due to the language's handling of pointer arithmetic, where operations on pointers are scaled by the size of the data type they point to. This can lead to referencing unintended memory locations if not carefully managed.

• Exploitation Methods:

• Attackers can exploit this vulnerability by manipulating pointers to read or write to incorrect memory locations.
• Common attack patterns include buffer overflows and memory corruption through incorrect indexing or scaling of pointers.

• Security Impact:

• Direct consequences include unexpected behavior in the program, data corruption, or crashes.
• Potential cascading effects could involve further memory corruption, leading to vulnerabilities like arbitrary code execution.
• Business impact might include data breaches, loss of sensitive information, and damage to system integrity.

• Prevention Guidelines:

• Specific code-level fixes involve ensuring correct pointer arithmetic and validating array bounds.
• Security best practices include using safer functions and constructs, such as std::vector in C++, to handle arrays.
• Recommended tools and frameworks include static analysis tools to detect pointer arithmetic issues and adopting memory-safe languages where possible.

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Technical Details

Likelihood of Exploit: Medium

Affected Languages: C, C++

Affected Technologies: Not specified

Vulnerable Code Example

// Vulnerable function demonstrating incorrect pointer scaling
#include <stdio.h>

void printArrayElements(int *arr, int size) {
    for (int i = 0; i < size; i++) {
        // Incorrect pointer arithmetic: incrementing by sizeof(int) instead of 1
        printf("%d\n", *(arr + i * sizeof(int)));
    }
}

int main() {
    int numbers[] = {10, 20, 30, 40, 50};
    printArrayElements(numbers, 5);
    return 0;
}

Explanation:

• The code incorrectly scales the pointer arithmetic by sizeof(int) in line 7. This results in the pointer moving by a factor of sizeof(int) squared, leading to incorrect memory access. The program may access unintended memory locations, potentially causing undefined behavior or crashes.

How to fix Incorrect Pointer Scaling?

To fix the incorrect pointer scaling issue:

1. Understand Pointer Arithmetic: In C, adding an integer to a pointer automatically scales the addition by the size of the type the pointer points to. Therefore, adding 1 to an int pointer moves the pointer by sizeof(int) bytes.
2. Remove Unnecessary Scaling: Avoid manually multiplying the index by sizeof(int) when using pointer arithmetic, as this is handled automatically by the compiler.

Fixed Code Example

// Secure function with correct pointer arithmetic
#include <stdio.h>

void printArrayElements(int *arr, int size) {
    for (int i = 0; i < size; i++) {
        // Correct pointer arithmetic: incrementing by 1
        printf("%d\n", *(arr + i));
    }
}

int main() {
    int numbers[] = {10, 20, 30, 40, 50};
    printArrayElements(numbers, 5);
    return 0;
}

Explanation:

• The fix involves removing the unnecessary multiplication by sizeof(int) in line 7. The pointer arithmetic now correctly advances the pointer by one element size for each iteration. This ensures safe and intended memory access, adhering to C's pointer arithmetic rules and preventing undefined behavior.