CWE-469 Base Draft Medium likelihood

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…

Definition

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.

Real-world impact

Real-world CVEs caused by CWE-469

No public CVE references are linked to this CWE in MITRE's catalog yet.

How attackers exploit it

Step-by-step attacker path

1
Identify a code path that handles untrusted input without validation.
2
Craft a payload that exercises the unsafe behavior — injection, traversal, overflow, or logic abuse.
3
Deliver the payload through a normal request and observe the application's reaction.
4
Iterate until the response leaks data, executes attacker code, or escalates privileges.

Vulnerable code example

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.

Vulnerable C

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* 
  ...

Secure code example

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.

Secure C

...
  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.

Prevention checklist

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.

Detection signals

How to detect CWE-469

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.

Automated Static Analysis High

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 auto-fix

Plexicus auto-detects CWE-469 and opens a fix PR in under 60 seconds.

Codex Remedium scans every commit, identifies this exact weakness, and ships a reviewer-ready pull request with the patch. No tickets. No hand-offs.

Get a demo Try Plexicus free

Frequently asked questions

What is CWE-469?

How serious is CWE-469?

MITRE rates the likelihood of exploit as Medium — exploitation is realistic but typically requires specific conditions.

What languages or platforms are affected by CWE-469?

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

How can I prevent 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.

How does Plexicus detect and fix CWE-469?

Plexicus's SAST engine matches the data-flow signature for CWE-469 on every commit. When a match is found, our Codex Remedium agent opens a fix PR with the corrected code, tests, and a one-line summary for the reviewer.

Where can I learn more about CWE-469?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/469.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-469

CWE-682 Parent

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Weigh You Down.

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Use of Pointer Subtraction to Determine Size

What is CWE-469?

Real-world CVEs caused by CWE-469

Step-by-step attacker path

Vulnerable C

Secure C

How to prevent CWE-469

How to detect CWE-469

Plexicus auto-detects CWE-469 and opens a fix PR in under 60 seconds.

Frequently asked questions

Weaknesses related to CWE-469

Incorrect Calculation

Wrap-around Error

Incorrect Calculation of Buffer Size

Incorrect Bitwise Shift of Integer

Insufficient Precision or Accuracy of a Real Number

Incorrect Calculation of Multi-Byte String Length

Integer Overflow or Wraparound

Integer Underflow (Wrap or Wraparound)

Off-by-one Error

Further reading

Don't Let Security
Weigh You Down.

Use of Pointer Subtraction to Determine Size

What is CWE-469?

Real-world CVEs caused by CWE-469

Step-by-step attacker path

Vulnerable C

Secure C

How to prevent CWE-469

How to detect CWE-469

Plexicus auto-detects CWE-469 and opens a fix PR in under 60 seconds.

Frequently asked questions

Weaknesses related to CWE-469

Incorrect Calculation

Wrap-around Error

Incorrect Calculation of Buffer Size

Incorrect Bitwise Shift of Integer

Insufficient Precision or Accuracy of a Real Number

Incorrect Calculation of Multi-Byte String Length

Integer Overflow or Wraparound

Integer Underflow (Wrap or Wraparound)

Off-by-one Error

Further reading

Don't Let SecurityWeigh You Down.

Don't Let Security
Weigh You Down.