CWE-789: Memory Allocation with Excessive Size Value

What is Memory Allocation with Excessive Size Value?

• Overview: Memory Allocation with Excessive Size Value (CWE-789) occurs when a program allocates memory based on a size value that is not properly validated, allowing potentially excessive amounts of memory to be allocated. This can lead to resource exhaustion and system instability.

• Exploitation Methods:

• Attackers can exploit this vulnerability by providing large or manipulated input values that the program uses to allocate memory.
• Common attack patterns include buffer overflows and denial of service (DoS) attacks by exhausting available memory resources.

• Security Impact:

• Direct consequences of successful exploitation include application crashes, system instability, and denial of service.
• Potential cascading effects may include data corruption, unauthorized access, and further exploitation of additional vulnerabilities.
• Business impact can involve service downtime, loss of customer trust, and potential financial losses due to system unavailability or data breaches.

• Prevention Guidelines:

• Specific code-level fixes include validating and constraining input size values before using them for memory allocation.
• Security best practices involve implementing input validation, limiting maximum allocation sizes, and using safe memory management techniques.
• Recommended tools and frameworks include static analysis tools to detect improper memory allocations and using memory-safe languages or libraries when possible.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: C, C++, Not Language-Specific

Affected Technologies: Not specified

Vulnerable Code Example

C Example for CWE-789: Memory Allocation with Excessive Size Value

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

void processData(size_t dataSize) {
    // Vulnerable: Allocating memory based on external input without validation
    char *buffer = (char *)malloc(dataSize);
    if (buffer == NULL) {
        fprintf(stderr, "Memory allocation failed\n");
        return;
    }

    // Simulated data processing
    // ...

    free(buffer);
}

int main() {
    size_t inputSize;
    printf("Enter the size of data: ");
    scanf("%zu", &inputSize);
    processData(inputSize);
    return 0;
}

Key Vulnerability

• Lack of Validation: The code allocates memory based on user input (dataSize) without validating if it's within a reasonable range. This can lead to excessive memory allocation, potentially exhausting system resources or leading to a denial of service.

How to fix Memory Allocation with Excessive Size Value?

To address this vulnerability, ensure that the size value used for memory allocation is validated against predefined limits. Implementing size checks avoids excessive memory allocations and potential denial of service attacks. The following steps should be followed:

1. Define a Maximum Allowable Size: Establish a sensible upper limit for memory allocation. This limit should align with the application's expected use case.

2. Validate Input: Before proceeding with memory allocation, check if the input size is within the allowable range.

3. Handle Invalid Input Gracefully: If the input size exceeds the maximum allowable size, handle the situation gracefully, such as by reporting an error to the user or logging the event.

Fixed Code Example

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

#define MAX_DATA_SIZE 1048576 // Maximum allowable size (e.g., 1 MB)

void processData(size_t dataSize) {
    // Fix: Validate dataSize before allocating memory
    if (dataSize > MAX_DATA_SIZE) {
        fprintf(stderr, "Requested size exceeds maximum limit\n");
        return;
    }

    char *buffer = (char *)malloc(dataSize);
    if (buffer == NULL) {
        fprintf(stderr, "Memory allocation failed\n");
        return;
    }

    // Simulated data processing
    // ...

    free(buffer);
}

int main() {
    size_t inputSize;
    printf("Enter the size of data: ");
    scanf("%zu", &inputSize);
    
    // Validate input to prevent excessive memory allocation
    processData(inputSize);
    return 0;
}

Key Fixes

• Maximum Size Definition: A constant MAX_DATA_SIZE is defined to set an upper limit on the data size that can be processed.
• Validation Check: Before allocating memory, the input size is checked against MAX_DATA_SIZE. If the size exceeds the limit, the function returns early with an error message.
• Safe Memory Allocation: This approach ensures that memory is only allocated if the size is within a safe and defined range, preventing excessive allocation and potential denial of service.