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.

Extended Description:
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.

Affected languages: Not Language-Specific
Parent weaknesses: CWE-664, CWE-691

Consequences:
  - Integrity: Modify Application Data

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 havin

Mitigations:
  - [Implementation] Use industry standard APIs to synchronize your code.

Demonstrative examples:
The following function attempts to acquire a lock in order to perform operations on a shared resource.
However, the code does not check the value returned by pthread_mutex_lock() for errors. If pthread_mutex_lock() cannot acquire the mutex for any reason, the function may introduce a race condition into the program and result in undefined behavior.
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); 

The following code intends to fork a process, then have both the parent and child processes print a single line.
One might expect the code to print out something like:
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");

Real-world examples:
  - CVE-2021-1782: Chain: improper locking (CWE-667) leads to race condition (CWE-362), as exploited in the wild per CISA KEV.
  - CVE-2009-0935: Attacker provides invalid address to a memory-reading function, causing a mutex to be unlocked twice