CWE-362: Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')

What is Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')?

• Overview: Race conditions occur when two or more concurrent code sequences access a shared resource without proper synchronization, leading to unpredictable results. This happens when a timing window allows one sequence to modify the resource while another is accessing it.

• Exploitation Methods:

• Attackers exploit race conditions by manipulating the timing of execution to gain unauthorized access, modify data, or disrupt operations.
• Common attack patterns include time-of-check to time-of-use (TOCTOU) vulnerabilities and manipulating thread scheduling to intercept or alter data.

• Security Impact:

• Direct consequences of successful exploitation include data corruption, unauthorized data access, or system crashes.
• Potential cascading effects could lead to further vulnerabilities being exploited, privilege escalation, or denial of service.
• Business impact may include loss of data integrity, reputational damage, and financial loss due to service interruptions or data breaches.

• Prevention Guidelines:

• Specific code-level fixes include using synchronization mechanisms like mutexes, semaphores, or locks to ensure exclusive access to shared resources.
• Security best practices involve designing software with concurrency in mind, thoroughly testing for race conditions, and using atomic operations where possible.
• Recommended tools and frameworks include static and dynamic analysis tools to detect race conditions, and employing languages or libraries that provide built-in concurrency safety features.

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Technical Details

Likelihood of Exploit: Medium

Affected Languages: C, C++, Java

Affected Technologies: Mobile, ICS/OT

Vulnerable Code Example

C Example

#include <stdio.h>
#include <pthread.h>

int shared_counter = 0;  // Shared resource

void* increment_counter(void* arg) {
    for (int i = 0; i < 1000000; i++) {
        // Vulnerable code: No synchronization
        // Multiple threads can simultaneously read and write to shared_counter
        shared_counter++;
    }
    return NULL;
}

int main() {
    pthread_t threads[2];
    
    // Create two threads that increment the shared counter
    pthread_create(&threads[0], NULL, increment_counter, NULL);
    pthread_create(&threads[1], NULL, increment_counter, NULL);

    // Wait for both threads to complete
    pthread_join(threads[0], NULL);
    pthread_join(threads[1], NULL);

    // The expected result is 2000000, but due to race conditions,
    // the actual result may be different
    printf("Final counter value: %d\n", shared_counter);

    return 0;
}

Explanation

In this example, the shared_counter is a global variable accessed by multiple threads without any synchronization mechanism. This can lead to a race condition where the threads interfere with each other's operations on shared_counter, resulting in an incorrect final value.

How to fix Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')?

To fix this race condition, we need to ensure that only one thread at a time can modify the shared resource. This can be achieved by using synchronization mechanisms such as mutexes (mutual exclusion locks). A mutex will lock the shared resource while one thread is using it and prevent other threads from accessing it until the lock is released. This ensures that the increment operation is atomic and that no race condition occurs.

Fixed Code Example

#include <stdio.h>
#include <pthread.h>

int shared_counter = 0;  // Shared resource
pthread_mutex_t counter_mutex;  // Mutex for synchronizing access

void* increment_counter(void* arg) {
    for (int i = 0; i < 1000000; i++) {
        // Lock the mutex before modifying the shared resource
        pthread_mutex_lock(&counter_mutex);
        
        // Safely increment the counter
        shared_counter++;
        
        // Unlock the mutex after modification
        pthread_mutex_unlock(&counter_mutex);
    }
    return NULL;
}

int main() {
    pthread_t threads[2];
    
    // Initialize the mutex before creating threads
    pthread_mutex_init(&counter_mutex, NULL);
    
    // Create two threads that increment the shared counter
    pthread_create(&threads[0], NULL, increment_counter, NULL);
    pthread_create(&threads[1], NULL, increment_counter, NULL);

    // Wait for both threads to complete
    pthread_join(threads[0], NULL);
    pthread_join(threads[1], NULL);

    // Destroy the mutex after threads are done
    pthread_mutex_destroy(&counter_mutex);

    printf("Final counter value: %d\n", shared_counter);

    return 0;
}

Explanation

In the fixed code example, a pthread_mutex_t object is initialized before creating the threads. The pthread_mutex_lock and pthread_mutex_unlock functions are used to ensure that only one thread can access the shared_counter at a time. This prevents race conditions and ensures that the final counter value is consistent and correct. Additionally, the mutex is properly destroyed after its use, which is a good practice for resource management.