CWE-401: Missing Release of Memory after Effective Lifetime

What is Missing Release of Memory after Effective Lifetime?

• Overview: Missing Release of Memory after Effective Lifetime refers to a situation where a program fails to properly release memory that has been allocated and is no longer needed, leading to memory leaks. This can occur in languages like C and C++ where developers manually manage memory allocation and deallocation.

• Exploitation Methods:

• Attackers may exploit memory leaks to exhaust system resources, leading to a denial of service (DoS).
• Attackers can repeatedly trigger code paths that allocate memory without deallocation to degrade system performance or crash the application.

• Security Impact:

• Direct consequences include reduced system performance and application crashes due to memory exhaustion.
• Potential cascading effects involve broader system instability if critical services are affected by the memory leaks.
• Business impact includes potential downtime, loss of user trust, and increased operational costs for managing and mitigating the leaks.

• Prevention Guidelines:

• Specific code-level fixes include ensuring every memory allocation is paired with a corresponding deallocation, using functions like free() in C/C++.
• Security best practices involve using smart pointers in C++ (such as std::unique_ptr and std::shared_ptr) to manage memory automatically.
• Recommended tools and frameworks include static analysis tools like Valgrind or AddressSanitizer to detect memory leaks during development and testing phases.

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Technical Details

Likelihood of Exploit: Medium

Affected Languages: C, C++

Affected Technologies: Not specified

Vulnerable Code Example

C Example

// Vulnerable code demonstrating a memory leak due to missing release of memory
#include <stdio.h>
#include <stdlib.h>

void process_data() {
    int *data = (int *)malloc(100 * sizeof(int));  // Allocate memory for 100 integers
    if (data == NULL) {
        fprintf(stderr, "Memory allocation failed\n");
        return; // Exit if memory allocation fails
    }

    // Simulate some processing on the data
    for (int i = 0; i < 100; i++) {
        data[i] = i * 2;
    }

    // Memory leak occurs because `data` is not released with free(data)
    // The allocated memory is not returned to the system, leading to a resource leak
}

Explanation:

• The code above allocates memory for an integer array but does not release it using free(data); after it is no longer needed. This results in a memory leak, as the allocated memory is not returned to the system for reuse.
• The absence of free(data); means that the program could consume more and more memory over time, potentially exhausting system resources.

How to fix Missing Release of Memory after Effective Lifetime?

To fix the memory leak issue, ensure that every malloc() call is paired with a corresponding free() call. This means that after you have finished using a dynamically allocated memory block, you must explicitly release it back to the system. Here are best practices to follow:

• Always check if malloc() returns NULL to handle memory allocation failures gracefully.
• Use free() to deallocate memory once it is no longer needed, ensuring that it is called in all execution paths, including error handling paths.
• Consider using tools like Valgrind to detect memory leaks during development and testing.

Fixed Code Example

// Fixed code with comments explaining the security controls implemented
#include <stdio.h>
#include <stdlib.h>

void process_data() {
    int *data = (int *)malloc(100 * sizeof(int));  // Allocate memory for 100 integers
    if (data == NULL) {
        fprintf(stderr, "Memory allocation failed\n");
        return; // Exit if memory allocation fails
    }

    // Simulate some processing on the data
    for (int i = 0; i < 100; i++) {
        data[i] = i * 2;
    }

    // Properly free the allocated memory after it is no longer needed
    free(data);  // Release the allocated memory to prevent memory leaks
}

Explanation:

• The fixed version ensures that free(data); is called after processing is complete, releasing the allocated memory and preventing a memory leak.
• This demonstrates good memory management practices by ensuring that all allocated resources are properly deallocated.
• By including free(data);, the code returns the allocated memory to the system, ensuring efficient use of resources and preventing potential memory exhaustion.