CWE-662: Improper Synchronization

Description

The product utilizes multiple threads, processes, components, or systems to allow temporary access to a shared resource that can only be exclusive to one process at a time, but it does not properly synchronize these actions, which might cause simultaneous accesses of this resource by multiple threads or processes.

Synchronization refers to a variety of behaviors and mechanisms that allow two or more independently-operating processes or threads to ensure that they operate on shared resources in predictable ways that do not interfere with each other. Some shared resource operations cannot be executed atomically; that is, multiple steps must be guaranteed to execute sequentially, without any interference by other processes. Synchronization mechanisms vary widely, but they may include locking, mutexes, and semaphores. When a multi-step operation on a shared resource cannot be guaranteed to execute independent of interference, then the resulting behavior can be unpredictable. Improper synchronization could lead to data or memory corruption, denial of service, etc.

Potential Impact

Demonstrative Examples

void f(pthread_mutex_t *mutex) {
                        pthread_mutex_lock(mutex);
                           
                           /* access shared resource */
                           
                           
                           pthread_mutex_unlock(mutex);
                     }

int f(pthread_mutex_t *mutex) {
                        int result;
                           result = pthread_mutex_lock(mutex);if (0 != result)return result;
                           
                           
                           /* access shared resource */
                           
                           
                           return pthread_mutex_unlock(mutex);
                     }

static void print (char * string) {
                        char * word;int counter;for (word = string; counter = *word++; ) {
                              putc(counter, stdout);fflush(stdout);
                                 /* Make timing window a little larger... */
                                 
                                 sleep(1);
                           }
                     }
                     int main(void) {
                        pid_t pid;
                           pid = fork();if (pid == -1) {exit(-2);}else if (pid == 0) {print("child\n");}else {print("PARENT\n");}exit(0);
                     }

Mitigations & Prevention

Detection Methods

• Automated Static Analysis — Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then sea

Real-World CVE Examples

Related Weaknesses

Taxonomy Mappings

• CERT C Secure Coding: SIG00-C — Mask signals handled by noninterruptible signal handlers
• CERT C Secure Coding: SIG31-C — Do not access shared objects in signal handlers
• CLASP: — State synchronization error
• The CERT Oracle Secure Coding Standard for Java (2011): VNA03-J — Do not assume that a group of calls to independently atomic methods is atomic
• Software Fault Patterns: SFP19 — Missing Lock