CWE-763: Release of Invalid Pointer or Reference

What is Release of Invalid Pointer or Reference?

• Overview: Release of Invalid Pointer or Reference (CWE-763) occurs when a software product incorrectly attempts to free memory by using the wrong memory release function or by improperly using the correct one, leading to memory management errors.

• Exploitation Methods:

• Attackers can exploit this vulnerability by triggering the incorrect release process, potentially leading to memory corruption.
• Common attack patterns include forcing the system to perform unauthorized actions or crash by manipulating memory management routines.

• Security Impact:

• Direct consequences of successful exploitation include application crashes, memory corruption, or denial of service.
• Potential cascading effects involve further memory leaks or execution of arbitrary code.
• Business impact can include loss of data integrity, reduced system availability, and damage to brand reputation.

• Prevention Guidelines:

• Specific code-level fixes include ensuring that memory allocation and deallocation use matching and compatible functions.
• Security best practices involve rigorous testing for memory management operations and code reviews to catch misuse.
• Recommended tools and frameworks include static analysis tools to detect improper memory management and using memory-safe languages or libraries where possible.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: C, C++

Affected Technologies: Not specified

Vulnerable Code Example

C Example

#include <stdio.h>
#include <stdlib.h>

void process_data(int *data) {
    // Process the data
    printf("Processing data: %d\n", *data);
}

int main() {
    int *data = (int *)malloc(sizeof(int));
    if (data == NULL) {
        fprintf(stderr, "Memory allocation failed\n");
        return 1;
    }
    
    *data = 42;
    process_data(data);

    // Incorrectly freeing the pointer twice
    free(data);  // First free
    free(data);  // Second free: Release of Invalid Pointer or Reference

    return 0;
}

Explanation:

• In the above code, the memory pointed to by data is freed twice. This double free can lead to undefined behavior, including memory corruption, application crashes, or potential security vulnerabilities if attackers exploit this behavior.

How to fix Release of Invalid Pointer or Reference?

To address the issue of releasing an invalid pointer or reference, ensure that each allocated memory block is freed only once, and set the pointer to NULL after freeing it. This prevents accidental double frees or use-after-free errors.

Specific Fixes:

1. Only call free() once for any allocated memory block.
2. Set the pointer to NULL immediately after freeing it to prevent accidental reuse or double freeing.

Fixed Code Example

#include <stdio.h>
#include <stdlib.h>

void process_data(int *data) {
    // Process the data
    printf("Processing data: %d\n", *data);
}

int main() {
    int *data = (int *)malloc(sizeof(int));
    if (data == NULL) {
        fprintf(stderr, "Memory allocation failed\n");
        return 1;
    }
    
    *data = 42;
    process_data(data);

    // Correctly freeing the pointer and setting it to NULL
    free(data);  // Free the allocated memory
    data = NULL; // Set the pointer to NULL after freeing

    return 0;
}

Explanation:

• In the fixed code, the memory is freed only once, and the pointer is immediately set to NULL. This ensures that any subsequent operations on the pointer do not lead to undefined behavior, such as double freeing or use-after-free errors. Setting the pointer to NULL is a defensive programming practice that helps prevent accidental misuse of the pointer after it has been freed.