Memory Allocation with Excessive Size Value

Description

Memory Allocation with Excessive Size Value is a resource management vulnerability where software allocates memory based on an untrusted or unchecked size value without ensuring the size is within acceptable limits. When applications accept size parameters from external sources (user input, network data, file content) and use them directly in allocation functions like malloc(), calloc(), or new, attackers can specify extremely large values. This can cause immediate allocation failures, out-of-memory conditions, or system-wide resource exhaustion leading to denial of service.

Risk

Excessive memory allocation has multiple attack vectors. Direct attacks specify huge allocation sizes to crash the application with out-of-memory errors or exhaust system memory affecting other processes. Integer overflow attacks cause size calculations to wrap around to small values, resulting in undersized buffers that lead to heap overflows when filled with actual data. Large allocations may also trigger performance degradation as the system swaps memory to disk. In shared hosting environments, excessive allocation can impact other applications. Some systems may hang or become unresponsive rather than failing cleanly.

Solution

Always validate allocation size parameters before use. Define and enforce maximum acceptable sizes based on application requirements. Check for integer overflow in size calculations before allocation. Use safe integer arithmetic functions or manual overflow checks. Handle allocation failures gracefully—don't assume malloc will always succeed. Use resource limits (ulimit, setrlimit) to contain damage from runaway allocations. Consider using memory pools with fixed maximum sizes. Implement request throttling for operations that trigger allocations. Log excessive allocation attempts for security monitoring.

Common Consequences

Impact	Details
Availability	Scope: Availability DoS: Resource Consumption (Memory) - Excessive allocations exhaust available memory, crashing the application or system.
Availability	Scope: Availability DoS: Crash - Out-of-memory conditions typically crash the application.
Integrity	Scope: Integrity Modify Memory - Integer overflow in size calculation may lead to undersized allocation and subsequent buffer overflow.

Example Code

Vulnerable Code

// Vulnerable: Unchecked allocation size from user input
#include <stdlib.h>
#include <string.h>

void vulnerable_alloc_user_size(unsigned int size) {
    // Vulnerable: No validation of size
    char* buffer = (char*)malloc(size);
    if (buffer == NULL) {
        // Handle error, but damage may already be done
        return;
    }

    // Use buffer...
    free(buffer);
}

// Attack: Pass size = 4294967295 (0xFFFFFFFF) to allocate 4GB

// Vulnerable: Integer overflow in size calculation
void vulnerable_alloc_array(unsigned int count) {
    // Vulnerable: Multiplication can overflow
    unsigned int totalBytes = count * sizeof(int);

    // If count = 1073741824 (0x40000000), totalBytes wraps to 0
    int* buffer = (int*)malloc(totalBytes);
    if (buffer == NULL) return;

    // Writes way past actual (tiny) allocation
    for (unsigned int i = 0; i < count; i++) {
        buffer[i] = 0;  // Heap overflow!
    }

    free(buffer);
}

// Vulnerable: Java HashMap with untrusted capacity
import java.util.HashMap;

public class VulnerableHashMap {
    public HashMap<String, String> createFromInput(int capacity) {
        // Vulnerable: No validation of capacity
        // Huge capacity causes OutOfMemoryError
        HashMap<String, String> map = new HashMap<>(capacity);
        return map;
    }
}

// Attack: Pass capacity = Integer.MAX_VALUE

// Vulnerable: Network data controls allocation
typedef struct {
    uint32_t data_length;
    uint32_t item_count;
} PacketHeader;

void vulnerable_process_packet(PacketHeader* header) {
    // Vulnerable: Trust header fields directly
    char* data = malloc(header->data_length);  // Could be huge
    Item* items = malloc(header->item_count * sizeof(Item));  // Overflow possible

    // ...
}

// Vulnerable: Signed/unsigned confusion
void vulnerable_signed_alloc(int size) {
    // Vulnerable: Negative int becomes huge unsigned value
    char* buffer = malloc(size);  // If size = -1, becomes SIZE_MAX

    // Allocation likely fails, but behavior varies
}

Fixed Code

// Fixed: Validate allocation size
#include <stdlib.h>
#include <stdint.h>

#define MAX_ALLOC_SIZE (64 * 1024 * 1024)  // 64 MB maximum

void* fixed_alloc_user_size(size_t size) {
    // Fixed: Validate size against maximum
    if (size == 0 || size > MAX_ALLOC_SIZE) {
        return NULL;  // Reject invalid sizes
    }

    void* buffer = malloc(size);
    return buffer;  // May still be NULL on allocation failure
}

// Fixed: Check for integer overflow
#include <stdint.h>

void* fixed_alloc_array(size_t count, size_t element_size) {
    // Fixed: Check for overflow before multiplication
    if (count == 0 || element_size == 0) {
        return NULL;
    }

    if (count > SIZE_MAX / element_size) {
        // Multiplication would overflow
        return NULL;
    }

    size_t total_bytes = count * element_size;

    // Additional sanity check
    if (total_bytes > MAX_ALLOC_SIZE) {
        return NULL;
    }

    return malloc(total_bytes);
}

// Alternative: Use calloc which has built-in overflow checking
void* fixed_alloc_array_v2(size_t count, size_t element_size) {
    if (count > MAX_ALLOC_SIZE / element_size) {
        return NULL;
    }

    // calloc checks for overflow internally
    return calloc(count, element_size);
}

// Fixed: Validate capacity in Java
import java.util.HashMap;

public class FixedHashMap {
    private static final int MAX_CAPACITY = 1000000;  // 1 million entries max

    public HashMap<String, String> createFromInput(int capacity)
            throws IllegalArgumentException {
        // Fixed: Validate capacity
        if (capacity < 0) {
            throw new IllegalArgumentException("Capacity cannot be negative");
        }
        if (capacity > MAX_CAPACITY) {
            throw new IllegalArgumentException("Capacity exceeds maximum: " + MAX_CAPACITY);
        }

        return new HashMap<>(capacity);
    }
}

// Fixed: Validate network data before allocation
#include <arpa/inet.h>  // For ntohl

#define MAX_DATA_LENGTH (1024 * 1024)  // 1 MB max
#define MAX_ITEM_COUNT 10000

typedef struct {
    uint32_t data_length;
    uint32_t item_count;
} PacketHeader;

int fixed_process_packet(PacketHeader* header) {
    // Fixed: Convert from network byte order
    uint32_t data_length = ntohl(header->data_length);
    uint32_t item_count = ntohl(header->item_count);

    // Fixed: Validate before allocation
    if (data_length > MAX_DATA_LENGTH) {
        return -1;  // Reject oversized data
    }

    if (item_count > MAX_ITEM_COUNT) {
        return -1;  // Reject too many items
    }

    // Fixed: Check for overflow in multiplication
    if (item_count > SIZE_MAX / sizeof(Item)) {
        return -1;
    }

    char* data = malloc(data_length);
    if (data == NULL && data_length > 0) {
        return -1;
    }

    Item* items = malloc(item_count * sizeof(Item));
    if (items == NULL && item_count > 0) {
        free(data);
        return -1;
    }

    // Process data...

    free(items);
    free(data);
    return 0;
}

// Fixed: Handle signed values properly
#include <stddef.h>

void* fixed_signed_alloc(ssize_t size) {
    // Fixed: Reject negative values
    if (size <= 0) {
        return NULL;
    }

    // Fixed: Validate against maximum
    if ((size_t)size > MAX_ALLOC_SIZE) {
        return NULL;
    }

    return malloc((size_t)size);
}

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CVE Examples

• CVE-2019-19911: Memory allocation with excessive size in image processing.
• CVE-2010-3701: Excessive memory allocation in virtualization software.
• CVE-2008-1708: Integer overflow leading to undersized allocation.
• CVE-2008-0977: Unchecked allocation size from network data.
• CVE-2006-3791: Large allocation request causing denial of service.
• CVE-2004-2589: Memory exhaustion via excessive allocation size.

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References

1. MITRE Corporation. "CWE-789: Memory Allocation with Excessive Size Value." https://cwe.mitre.org/data/definitions/789.html
2. CERT C Coding Standard. "MEM35-C. Allocate sufficient memory for an object."
3. CERT C Coding Standard. "INT30-C. Ensure that unsigned integer operations do not wrap."