Improper Synchronization

The product utilizes multiple threads or processes 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.


The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.

Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.

Example One

The following function attempts to acquire a lock in order to perform operations on a shared resource.

void f(pthread_mutex_t *mutex) {


  /* access 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.

In order to avoid data races, correctly written programs must check the result of thread synchronization functions and appropriately handle all errors, either by attempting to recover from them or reporting them to higher levels.

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);


Example Two

The following code intends to fork a process, then have both the parent and child processes print a single line.

static void print (char * string) {

  char * word;
  int counter;
  for (word = string; counter = *word++; ) {

    putc(counter, stdout);
    /* Make timing window a little larger... */




int main(void) {

  pid_t pid;

  pid = fork();
  if (pid == -1) {
  else if (pid == 0) {
  else {


One might expect the code to print out something like:



However, because the parent and child are executing concurrently, and stdout is flushed each time a character is printed, the output might be mixed together, such as:


[blank line]

[blank line]

See Also

Comprehensive Categorization: Resource Lifecycle Management

Weaknesses in this category are related to resource lifecycle management.

CISQ Quality Measures - Security

Weaknesses in this category are related to the CISQ Quality Measures for Security. Presence of these weaknesses could reduce the security of the software.

CISQ Quality Measures - Reliability

Weaknesses in this category are related to the CISQ Quality Measures for Reliability. Presence of these weaknesses could reduce the reliability of the software.

Comprehensive CWE Dictionary

This view (slice) covers all the elements in CWE.

CISQ Data Protection Measures

This view outlines the SMM representation of the Automated Source Code Data Protection Measurement specifications, as identified by the Consortium for Information & So...

Entries with Maintenance Notes

CWE entries in this view have maintenance notes. Maintenance notes are an indicator that an entry might change significantly in future versions. This view was created...

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