CWE-820: Missing Synchronization

Code Examples & CVEs

Demonstrative Examples

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);                      }

Source-backed guidance

Additional facts reviewed against primary or authoritative security sources.

Detect imprecise mappings involving CWE-820

Review mappings to CWE-820, Missing Synchronization, with MITRE's mapping and navigation criteria. Flag any selection that points to a View or Category, remains at a higher abstraction than the available evidence supports, or ignores relevant parent, child, peer, and alternative entries. Treat those findings as mapping-quality defects, correct them before publication, and retain the comparison trail for repeatable audits.

CWE Mapping and Navigation Guidance — MITRE CWE

Prevent CWE-820 through an SSDF control plan

Use NIST SSDF practices to make prevention of CWE-820, Missing Synchronization, an explicit development outcome. Translate the CWE definition into security requirements and design constraints, choose safer implementation patterns and toolchain checks, and define acceptance evidence before release. Feed every confirmed occurrence back into the requirements, design review, and coding rules so the same root cause is removed across the product rather than patched in one location.

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

Triage CWE-820 against known exploitation evidence

Use CISA's Known Exploited Vulnerabilities catalog to test whether a vulnerability mapped to CWE-820, Missing 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

Use MITRE taxonomy anchors to review Missing Synchronization

Recorded impacts include Modify Application Data, Read Application Data, and Alter Execution Logic; related weaknesses include CWE-662. Use these source-defined anchors to turn CWE-820 into implementation, review, and verification checks for the affected component.

CWE-820: Missing Synchronization — MITRE CWE

Validate CWE-820 with root-cause mapping checks

Apply MITRE's root-cause mapping quick tips to CWE-820, Missing 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-820: Missing Synchronization?+

CWE-820: Missing Synchronization is a Common Weakness Enumeration (CWE) entry maintained by MITRE. The product utilizes a shared resource in a concurrent manner but does not attempt to synchronize access to the resource. If access to a shared resource is not synchronized, then the resource may not be in a state that is expected by the product. This might lead to unexpected or insecure behaviors, especially if an attacker can influence the shared resource.

What are the security consequences of Missing Synchronization?+

If exploited, CWE-820 (Missing Synchronization) it can compromise Integrity, Confidentiality and Other, leading to outcomes such as Modify Application Data, Read Application Data and Alter Execution Logic.

Which programming languages are affected by Missing Synchronization?+

CWE-820 commonly affects Not Language-Specific. Note that weaknesses are often language-agnostic patterns, so secure coding practices apply broadly.

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

A CWE (Common Weakness Enumeration) like CWE-820 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-820: Missing Synchronization

Extended Description

Technical Details

Applicable To

Security Consequences

Scope

Impact

Mitigation Strategies

Detection Methods