CWE-662: Improper Synchronization

ClassDraft

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.

View on MITRE

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.

Code Examples & CVEs

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.

BadC

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

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

GoodC

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);                      }

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:

BadC

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);                      }

Observed CVE Examples (2)

CVE-2021-1782

Chain: improper locking (CWE-667) leads to race condition (CWE-362), as exploited in the wild per CISA KEV.

View Details

CVE-2009-0935

Attacker provides invalid address to a memory-reading function, causing a mutex to be unlocked twice

View Details

Source-backed guidance

Additional facts reviewed against primary or authoritative security sources.

Verify controls for CWE-662 with SSDF evidence

Use NIST SSDF verification and vulnerability-response practices to detect CWE-662, Improper Synchronization, throughout the product lifecycle. Derive review questions, static or dynamic checks, and negative tests from the CWE's causal behavior; define the components and lifecycle stages each check covers; and retain findings with enough evidence to distinguish the root cause from symptoms and impacts. Track escapes and false negatives, then improve the verification plan after every confirmed occurrence.

NIST SP 800-218 Secure Software Development Framework — National Institute of Standards and Technology

Address Improper Synchronization during Implementation

MITRE associates mitigation with Implementation; documented detection approaches include Automated Static Analysis; recorded impacts include Modify Application Data, Read Application Data, and Alter Execution Logic. Use these source-defined anchors to turn CWE-662 into implementation, review, and verification checks for the affected component.

CWE-662: Improper Synchronization — MITRE CWE

Triage CWE-662 against known exploitation evidence

Use CISA's Known Exploited Vulnerabilities catalog to test whether a vulnerability mapped to CWE-662, Improper Synchronization, has evidence of exploitation in the wild. Confirm the CVE-to-CWE root-cause mapping independently before attaching the example, then capture the affected product, required action, and remediation deadline. A missing KEV match is not evidence that the weakness is unexploited, and a KEV entry must not be generalized to every occurrence of this CWE.

Known Exploited Vulnerabilities Catalog — Cybersecurity and Infrastructure Security Agency

Apply precise root-cause mapping to CWE-662

Apply MITRE's full root-cause mapping guidance when using CWE-662, Improper Synchronization. Separate weakness language from attacker prerequisites and technical impact, check the entry's abstraction and vulnerability-mapping notes, and prefer the most specific Base or Variant supported by the evidence. Record the rejected alternatives and require an independent review before the mapping is used for remediation trends or program metrics.

CVE to CWE Root Cause Mapping Guidance — MITRE CWE

Validate CWE-662 with root-cause mapping checks

Apply MITRE's root-cause mapping quick tips to CWE-662, Improper Synchronization. Confirm the finding describes the causal weakness rather than an impact or attack pattern, compare the abstraction and mapping notes with plausible alternatives, and have a second reviewer challenge the selection. Preserve the evidence and reasoning so recurring defects can be measured against one consistent identifier.

CVE to CWE Root Cause Mapping Quick Tips — MITRE CWE

Frequently Asked Questions

What is CWE-662: Improper Synchronization?+

CWE-662: Improper Synchronization is a Common Weakness Enumeration (CWE) entry maintained by MITRE. 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.

What are the security consequences of Improper Synchronization?+

If exploited, CWE-662 (Improper Synchronization) it can compromise Integrity, Confidentiality and Other, leading to outcomes such as Modify Application Data, Read Application Data and Alter Execution Logic.

How do you prevent or mitigate Improper Synchronization?+

Recommended mitigations for CWE-662 include: Use industry standard APIs to synchronize your code.

Which programming languages are affected by Improper Synchronization?+

CWE-662 commonly affects Not Language-Specific. Note that weaknesses are often language-agnostic patterns, so secure coding practices apply broadly.

What are real-world examples of Improper Synchronization?+

MITRE documents real CVEs mapped to CWE-662, including CVE-2021-1782 and CVE-2009-0935. You can look up the full details of each CVE, including CVSS scores and remediation guidance, on our CVE Lookup tool.

What is the difference between a CWE and a CVE?+

A CWE (Common Weakness Enumeration) like CWE-662 describes a category of software weakness — the underlying flaw type. A CVE (Common Vulnerabilities and Exposures) identifies a specific, real-world vulnerability in a particular product. In short, a CWE is the kind of mistake, and a CVE is an instance of that mistake being found in software.

CWE-662: Improper Synchronization

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