What is Use of Pointer Subtraction to Determine (CWE-469)?

TL;DR: Use of Pointer Subtraction to Determine Size (CWE-469) is a vulnerability that occurs when the difference between two pointers is used incorrectly, leading to potential memory corruption. To fix it, use an index variable instead.

What is Use of Pointer Subtraction to Determine Size?

Use of Pointer Subtraction to Determine Size (CWE-469) is a type of vulnerability that occurs when the product subtracts one pointer from another in order to determine size, but this calculation can be incorrect if the pointers do not exist in the same memory chunk. As defined by the MITRE Corporation under CWE-469.

Quick Summary

Use of Pointer Subtraction to Determine Size is a critical vulnerability that occurs when two pointers are subtracted incorrectly, leading to potential memory corruption and arbitrary code execution. This can compromise system integrity and confidentiality. Jump to: Overview · How It Works · Business Impact · Attack Scenario · Detection · Fixing · Framework-Specific Fixes · Ask AI · Best Practices · FAQ

Jump to: Quick Summary · Use of Pointer Subtraction to Determine Size Overview · How Use of Pointer Subtraction to Determine Size Works · Business Impact of Use of Pointer Subtraction to Determine Size · Use of Pointer Subtraction to Determine Size Attack Scenario · How to Detect Use of Pointer Subtraction to Determine Size · How to Fix Use of Pointer Subtraction to Determine Size · Framework-Specific Fixes for Use of Pointer Subtraction to Determine Size · How to Ask AI to Check Your Code for Use of Pointer Subtraction to Determine Size · Use of Pointer Subtraction to Determine Size Best Practices Checklist · Use of Pointer Subtraction to Determine Size FAQ · Vulnerabilities Related to Use of Pointer Subtraction to Determine Size · References · Scan Your Own Site

Use of Pointer Subtraction to Determine Size Overview

What: Use of Pointer Subtraction to Determine Size is a vulnerability where the difference between two pointers is used incorrectly.

Why it matters: Incorrect pointer subtraction can lead to memory corruption and arbitrary code execution, compromising system integrity.

Where it occurs: This weakness commonly appears in C/C++ applications that perform complex memory management operations.

Who is affected: Developers working with low-level languages like C and C++ are at risk if they do not validate pointer arithmetic correctly.

Who is NOT affected: Applications written in high-level languages (e.g., Python, Java) that abstract away pointer manipulation are generally immune to this issue.

How Use of Pointer Subtraction to Determine Size Works

Root Cause

The root cause lies in the incorrect calculation of size using pointer subtraction. When pointers do not exist within the same memory chunk, their difference can be inaccurate and lead to buffer overflows or other memory corruption issues.

Attack Flow

1. An attacker identifies a function that performs pointer arithmetic.
2. The attacker manipulates input data to cause an incorrect pointer subtraction.
3. This leads to memory corruption or arbitrary code execution.

Prerequisites to Exploit

• The application must perform pointer arithmetic without proper validation.
• Input data can be manipulated by the attacker to trigger the vulnerability.

Vulnerable Code

int main() {
    char *ptr1 = (char *)malloc(5);
    char *ptr2 = ptr1 + 3;
    int size = ptr2 - ptr1; // Incorrect pointer subtraction
}

This code is vulnerable because it subtracts two pointers without ensuring they are in the same memory chunk.

Secure Code

int main() {
    char *ptr1 = (char *)malloc(5);
    char *ptr2 = ptr1 + 3;
    int index = 0;
    for (; ptr1[index] != '\0'; ++index) {}
    int size = index; // Safe calculation of size using an index variable
}

The secure code uses an index variable to safely calculate the size, avoiding incorrect pointer subtraction.

Business Impact of Use of Pointer Subtraction to Determine Size

Confidentiality: Data confidentiality can be compromised if memory corruption leads to unauthorized access. Integrity: System integrity is at risk due to potential buffer overflows and arbitrary code execution. Availability: The application may crash or become unresponsive, impacting system availability.

• Financial loss
• Compliance violations
• Reputational damage

Use of Pointer Subtraction to Determine Size Attack Scenario

1. An attacker identifies a function that calculates the size using pointer subtraction.
2. They manipulate input data to cause an incorrect calculation.
3. This leads to memory corruption, potentially allowing arbitrary code execution.

How to Detect Use of Pointer Subtraction to Determine Size

Manual Testing

• Review functions performing pointer arithmetic for proper validation.
• Ensure pointers are within the same memory chunk before subtraction.

Automated Scanners (SAST / DAST)

Static analysis can identify incorrect pointer operations. Dynamic testing is necessary to confirm vulnerabilities in runtime environments.

PenScan Detection

PenScan’s scanner engines, such as ZAP and Nuclei, can detect this vulnerability during static code analysis and dynamic testing.

False Positive Guidance

False positives may occur if the pattern looks risky but is safe due to context a scanner cannot determine. Verify that pointers are within the same memory chunk before subtraction.

How to Fix Use of Pointer Subtraction to Determine Size

• Save an index variable.
• Validate pointer arithmetic operations before use.

Framework-Specific Fixes for Use of Pointer Subtraction to Determine Size

C/C++

int main() {
    char *ptr1 = (char *)malloc(5);
    char *ptr2 = ptr1 + 3;
    int index = 0;
    for (; ptr1[index] != '\0'; ++index) {}
    int size = index; // Safe calculation of size using an index variable
}

How to Ask AI to Check Your Code for Use of Pointer Subtraction to Determine Size

Use of Pointer Subtraction to Determine Size Best Practices Checklist

✅ Save an index variable instead of subtracting pointers. ✅ Validate pointer arithmetic operations before use.

Use of Pointer Subtraction to Determine Size FAQ

How does Use of Pointer Subtraction to Determine Size occur in C/C++ code?

It occurs when the difference between two pointers is calculated incorrectly, leading to potential memory corruption.

Can you provide an example of vulnerable code for Use of Pointer Subtraction to Determine Size?

Vulnerable code subtracts one pointer from another without ensuring they are in the same memory chunk.

How can I prevent Use of Pointer Subtraction to Determine Size in my C/C++ application?

Use an index variable instead of pointer subtraction and validate its value before using it.

What is the impact if Use of Pointer Subtraction to Determine Size is exploited?

It may lead to arbitrary code execution with privileges of the vulnerable program.

How does PenScan detect Use of Pointer Subtraction to Determine Size in my application?

static analysis and runtime testing can identify incorrect pointer subtraction operations.

What are some common false positives when detecting Use of Pointer Subtraction to Determine Size?

Scanners may flag correct pointer arithmetic as a vulnerability if they do not understand the context.

How does Use of Pointer Subtraction to Determine Size relate to other vulnerabilities in C/C++?

It often coexists with buffer overflows and memory corruption issues.

Vulnerabilities Related to Use of Pointer Subtraction to Determine Size

References

• MITRE
• NVD

Scan Your Own Site

Manual code review catches what you know to look for. An automated scan catches what you didn’t. Scan your own website using PenScan to find Use of Pointer Subtraction to Determine Size and other risks before an attacker does.