CWE-366: Race Condition within a Thread

What is Race Condition within a Thread?

• Overview: Race Condition within a Thread (CWE-366) occurs when multiple threads attempt to access and modify shared resources concurrently without proper synchronization, leading to unpredictable and incorrect program behavior.

• Exploitation Methods:

• Attackers can exploit this vulnerability by manipulating the timing of thread execution to access resources in an unintended sequence.
• Common attack patterns include forcing a thread to access a resource out of order, leading to data corruption or unauthorized access.

• Security Impact:

• Direct consequences of successful exploitation include data corruption, application crashes, and unintended behavior.
• Potential cascading effects involve system instability and security breaches due to corrupted data states.
• Business impact may include loss of data integrity, compromised system reliability, and reputational damage.

• Prevention Guidelines:

• Specific code-level fixes involve implementing proper locking mechanisms such as mutexes, semaphores, or other synchronization primitives.
• Security best practices include designing software to minimize shared resource use and ensuring atomic operations on shared data.
• Recommended tools and frameworks include static analysis tools to detect race conditions and using language-specific concurrency libraries that provide safe access to shared resources.

Corgea can automatically detect and fix Race Condition within a Thread in your codebase. Try Corgea free today.

Technical Details

Likelihood of Exploit: Medium

Affected Languages: C, C++, Java, C#

Affected Technologies: Not specified

Vulnerable Code Example

// This example demonstrates a race condition vulnerability.
// Multiple threads increment a shared counter without synchronization,
// leading to unpredictable results due to concurrent access.

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

#define NUM_THREADS 10
#define NUM_ITERATIONS 1000

int counter = 0; // Shared resource

void* increment_counter(void* arg) {
    for (int i = 0; i < NUM_ITERATIONS; i++) {
        counter++; // {12} Vulnerable line: Incrementing shared variable without lock
    }
    return NULL;
}

int main() {
    pthread_t threads[NUM_THREADS];

    // Create threads
    for (int i = 0; i < NUM_THREADS; i++) {
        if (pthread_create(&threads[i], NULL, increment_counter, NULL) != 0) {
            fprintf(stderr, "Error creating thread\n");
            return 1;
        }
    }

    // Wait for threads to finish
    for (int i = 0; i < NUM_THREADS; i++) {
        if (pthread_join(threads[i], NULL) != 0) {
            fprintf(stderr, "Error joining thread\n");
            return 1;
        }
    }

    printf("Final counter value: %d\n", counter); // {15} Result is unpredictable due to race condition
    return 0;
}

How to fix Race Condition within a Thread?

To fix the race condition, the shared resource needs to be accessed in a mutually exclusive manner. This can be achieved by using synchronization mechanisms such as mutexes. A mutex will ensure that only one thread can modify the shared resource at a time, preventing the race condition. Here is how you can implement this fix:

1. Initialize a pthread_mutex_t variable to act as a lock for the shared resource.
2. Use pthread_mutex_lock() before accessing the shared resource and pthread_mutex_unlock() after accessing it.
3. This ensures that when one thread is incrementing the counter, other threads are blocked until the first thread finishes.

Fixed Code Example

// Fixed version: Uses mutex to ensure exclusive access to the shared counter.

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

#define NUM_THREADS 10
#define NUM_ITERATIONS 1000

int counter = 0; // Shared resource
pthread_mutex_t counter_mutex = PTHREAD_MUTEX_INITIALIZER; // {11} Initialize mutex

void* increment_counter(void* arg) {
    for (int i = 0; i < NUM_ITERATIONS; i++) {
        pthread_mutex_lock(&counter_mutex); // {14} Lock the mutex before accessing the shared resource
        counter++; // Safely increment the shared counter
        pthread_mutex_unlock(&counter_mutex); // {17} Unlock the mutex after accessing the shared resource
    }
    return NULL;
}

int main() {
    pthread_t threads[NUM_THREADS];

    // Create threads
    for (int i = 0; i < NUM_THREADS; i++) {
        if (pthread_create(&threads[i], NULL, increment_counter, NULL) != 0) {
            fprintf(stderr, "Error creating thread\n");
            return 1;
        }
    }

    // Wait for threads to finish
    for (int i = 0; i < NUM_THREADS; i++) {
        if (pthread_join(threads[i], NULL) != 0) {
            fprintf(stderr, "Error joining thread\n");
            return 1;
        }
    }

    printf("Final counter value: %d\n", counter); // Result is now predictable and correct
    pthread_mutex_destroy(&counter_mutex); // {21} Clean up the mutex
    return 0;
}

In this fixed version, the use of a mutex ensures that only one thread at a time can modify the counter variable, thus preventing the race condition and ensuring that the final counter value is consistent and correct. Additionally, error handling for thread creation and joining has been added to follow best practices.