The product does not properly check when a function or operation returns a value that is legitimate for the function, but is not expected by the product.
View on MITRENo mitigation information available for this CWE.
No detection method information available for this CWE.
Certain packets (zero byte and other lengths) cause a recvfrom call to produce an unexpected return code that causes a server's listening loop to exit.
View DetailsKernel function does not properly handle when a null is returned by a function call, causing it to call another function that it shouldn't.
View DetailsMemory not properly cleared when read() function call returns fewer bytes than expected.
View DetailsBypass access restrictions when connecting from IP whose DNS reverse lookup does not return a hostname.
View DetailsBypass access restrictions when connecting from IP whose DNS reverse lookup does not return a hostname.
View DetailsGame server doesn't check return values for functions that handle text strings and associated size values.
View DetailsAdditional facts reviewed against primary or authoritative security sources.
Documented detection approaches include Automated Static Analysis; recorded impacts include Unexpected State, and Alter Execution Logic; observed examples include CVE-2004-1395, CVE-2002-2124, and CVE-2005-2553. Use these source-defined anchors to turn CWE-394 into implementation, review, and verification checks for the affected component.
CWE-394: Unexpected Status Code or Return Value — MITRE CWEUse NIST SSDF practices to make prevention of CWE-394, Unexpected Status Code or Return Value, 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 TechnologyUse CISA's Known Exploited Vulnerabilities catalog to test whether a vulnerability mapped to CWE-394, Unexpected Status Code or Return Value, 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 AgencyApply MITRE's full root-cause mapping guidance when using CWE-394, Unexpected Status Code or Return Value. 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 CWEApply MITRE's root-cause mapping quick tips to CWE-394, Unexpected Status Code or Return Value. 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 CWECWE-394: Unexpected Status Code or Return Value is a Common Weakness Enumeration (CWE) entry maintained by MITRE. The product does not properly check when a function or operation returns a value that is legitimate for the function, but is not expected by the product.
If exploited, CWE-394 (Unexpected Status Code or Return Value) it can compromise Integrity and Other, leading to outcomes such as Unexpected State and Alter Execution Logic.
CWE-394 commonly affects Not Language-Specific. Note that weaknesses are often language-agnostic patterns, so secure coding practices apply broadly.
MITRE documents real CVEs mapped to CWE-394, including CVE-2004-1395, CVE-2002-2124, CVE-2005-2553, CVE-2005-1858 and CVE-2000-0536. You can look up the full details of each CVE, including CVSS scores and remediation guidance, on our CVE Lookup tool.
A CWE (Common Weakness Enumeration) like CWE-394 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.