CWE-469: Use of Pointer Subtraction to Determine Size

How it's found

Use of Pointer Subtraction to Determine Size is typically found by tracing untrusted input from where it enters the system to the point where it is used without the check or neutralization this weakness describes, combining manual code review with dynamic testing.

Vulnerable vs. safe

int data;struct node* next;

tail = current;current = current->next;struct node* current = head;struct node* tail;while (current != NULL) {}return tail - head;
// Returns the number of nodes in a linked list from

// the given pointer to the head of the list.

// other methods for manipulating the liststruct node {};int size(struct node* head) {}...

count++;current = current->next;struct node* current = head;int count = 0;while (current != NULL) {}return count;...int size(struct node* head) {}

Consequences

• Modify Memory, Read Memory, Execute Unauthorized Code or Commands, Gain Privileges or Assume Identity: There is the potential for arbitrary code execution with privileges of the vulnerable program.

Mitigations

• 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.

Where this fits in a TurboPentest engagement

This weakness is not covered by the automated black-box pentest. IntegSec pentesters cover it in a manual engagement.

Frequently asked questions

Related CWEs

• Pillar weakness
  CWE-682: Incorrect Calculation