What is Free of Memory not on the Heap (CWE-590)?

TL;DR: Free of Memory not on the Heap (CWE-590) occurs when a program frees memory without verifying its allocation origin, leading to potential crashes or code execution. Ensure proper tracking and validation of memory allocations.

What is Free of Memory not on the Heap?

Free of Memory not on the Heap (CWE-590) is a type of memory management vulnerability that occurs when a program attempts to free memory using functions like free() without ensuring the memory was allocated with corresponding heap allocation functions such as malloc(), calloc(), or realloc(). As defined by the MITRE Corporation under CWE-590, and classified by the OWASP Foundation under [mapping]…

Quick Summary

Free of Memory not on the Heap is a critical vulnerability that can lead to undefined behavior, crashes, or allow attackers to execute arbitrary code. It occurs when memory allocated outside the heap is freed using functions designed for heap memory management.

Jump to: Overview · How it Works · Business Impact · Attack Scenario · Detection · Fixes

Jump to: Quick Summary · Free of Memory not on the Heap Overview · How Free of Memory not on the Heap Works · Business Impact of Free of Memory not on the Heap · Free of Memory not on the Heap Attack Scenario · How to Detect Free of Memory not on the Heap · How to Fix Free of Memory not on the Heap · Framework-Specific Fixes for Free of Memory not on the Heap · How to Ask AI to Check Your Code for Free of Memory not on the Heap · Free of Memory not on the Heap Best Practices Checklist · Free of Memory not on the Heap FAQ · Vulnerabilities Related to Free of Memory not on the Heap · References · Scan Your Own Site

Free of Memory not on the Heap Overview

What

Free of Memory not on the Heap occurs when a program attempts to free memory that was allocated outside the heap using functions like free().

Why it matters

This can lead to undefined behavior, crashes, or allow attackers to execute arbitrary code. It is critical for maintaining system integrity and security.

Where it occurs

It typically occurs in C/C++ applications where developers mistakenly use free() on memory that was not allocated via heap functions like malloc().

Who is affected

Developers using C/C++ who rely heavily on manual memory management are most at risk.

Who is NOT affected

Languages with automatic garbage collection, such as Java or Python, do not suffer from this issue due to their managed memory environments.

How Free of Memory not on the Heap Works

Root Cause

The root cause lies in freeing memory that was allocated outside the heap without proper validation. This can lead to undefined behavior and security vulnerabilities.

Attack Flow

1. An attacker identifies a pointer pointing to non-heap allocated memory.
2. The attacker triggers the program to free this memory using free().
3. Undefined behavior occurs, potentially leading to crashes or code execution.

Prerequisites to Exploit

• A pointer must point to non-heap allocated memory.
• The program must attempt to free this memory without proper validation.

Vulnerable Code

void example_function(int *ptr) {
    // Assume ptr points to non-heap allocated memory
    free(ptr);  // Incorrect usage of free()
}

This code is vulnerable because it attempts to free a pointer that was not allocated using heap functions, leading to undefined behavior.

Secure Code

void example_function(int *ptr) {
    if (is_heap_allocated(ptr)) {  // Ensure ptr points to valid heap memory
        free(ptr);
    } else {
        // Handle error or log invalid memory usage
    }
}

This code is secure because it verifies that the pointer was allocated using a heap function before attempting to free it.

Business Impact of Free of Memory not on the Heap

Confidentiality

• Exposed sensitive data if pointers point to areas containing user information.

Integrity

• Unauthorized modifications or corruption of critical data structures in memory.

Availability

• System crashes leading to service disruptions.

Business Consequences:

• Financial losses due to system downtime and recovery efforts.
• Compliance penalties for security breaches.
• Damage to reputation from publicized vulnerabilities.

Free of Memory not on the Heap Attack Scenario

1. An attacker identifies a pointer pointing to non-heap allocated memory in an application.
2. The attacker triggers the program to free this memory using free().
3. This leads to undefined behavior, potentially causing a crash or allowing arbitrary code execution.
4. The attacker exploits the resulting vulnerability to gain unauthorized access.

How to Detect Free of Memory not on the Heap

Manual Testing

• Review all instances where free() is called.
• Ensure each pointer passed to free() was allocated using heap functions like malloc().
• Check for proper validation before freeing memory.

Automated Scanners (SAST / DAST)

Static analysis can identify direct calls to free() without corresponding allocations. Dynamic testing requires observing actual runtime behavior and interactions.

PenScan Detection

PenScan’s scanner engines such as ZAP, Nuclei, Wapiti, Nikto, SSLyze, Dalfox, and Nmap can detect instances of Free of Memory not on the Heap during automated scans.

False Positive Guidance

A false positive occurs when a pointer is correctly allocated but appears to be freed without validation due to complex code paths or compiler optimizations. Ensure proper context review before marking as false positives.

How to Fix Free of Memory not on the Heap

• Only free pointers that were previously allocated using heap functions.
• Track which pointers point at valid chunks and free them only once.
• Use vetted libraries or frameworks that provide protection against freeing invalid pointers.
• Employ languages with automatic memory management for safer coding practices.

Framework-Specific Fixes for Free of Memory not on the Heap

C/C++

void example_function(int *ptr) {
    if (is_heap_allocated(ptr)) {  // Ensure ptr points to valid heap memory
        free(ptr);
    } else {
        // Handle error or log invalid memory usage
    }
}

How to Ask AI to Check Your Code for Free of Memory not on the Heap

Free of Memory not on the Heap Best Practices Checklist

✅ Ensure all pointers passed to free() were allocated with heap functions. ✅ Implement tracking mechanisms for valid heap allocations. ✅ Use vetted libraries or frameworks that protect against invalid pointer usage. ✅ Employ languages with automatic memory management when possible.

Free of Memory not on the Heap FAQ

How does freeing memory allocated elsewhere lead to security vulnerabilities?

Freeing memory that was not allocated using heap functions like malloc can cause undefined behavior, potentially leading to crashes or arbitrary code execution.

Can you provide an example of vulnerable code for CWE-590?

Vulnerable C code might include freeing a pointer without verifying if it was allocated with the corresponding heap function.

What is the primary mitigation strategy for Free of Memory not on the Heap?

Ensure that only pointers allocated using functions like malloc are freed, and track which pointers point to valid memory chunks.

How does Free of Memory not on the Heap affect system integrity?

It can lead to unauthorized modifications or corruption of critical data structures in memory.

What is the difference between freeing a pointer and reallocating it?

reallocating involves changing the size of an existing allocation, while free releases allocated memory back to the heap. Incorrect use of either can cause issues.

How does Free of Memory not on the Heap relate to other CWEs like Write-what-where Condition (CWE-123)?

Freeing invalid pointers can create write-what-where conditions, allowing attackers to overwrite memory with arbitrary values.

What are some real-world consequences of a Free of Memory not on the Heap vulnerability?

It can lead to data corruption, system crashes, or unauthorized code execution, impacting business operations and security.

Vulnerabilities Related to Free of Memory not on the Heap

References

https://cwe.mitre.org/data/definitions/590.html

• 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 Free of Memory not on the Heap and other risks before an attacker does.