CWE-636: Not Failing Securely ('Failing Open')

Extended Description

By entering a less secure state, the product inherits the weaknesses associated with that state, making it easier to compromise. At the least, it causes administrators to have a false sense of security. This weakness typically occurs as a result of wanting to "fail functional" to minimize administration and support costs, instead of "failing safe."

Source-backed guidance

Additional facts reviewed against primary or authoritative security sources.

Verify controls for CWE-636 with SSDF evidence

Use NIST SSDF verification and vulnerability-response practices to detect CWE-636, Not Failing Securely ('Failing Open'), 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 Not Failing Securely ('Failing Open') during Architecture and Design

MITRE associates mitigation with Architecture and Design; recorded impacts include Bypass Protection Mechanism; observed examples include CVE-2007-5277, and CVE-2006-4407. Use these source-defined anchors to turn CWE-636 into implementation, review, and verification checks for the affected component.

CWE-636: Not Failing Securely ('Failing Open') — MITRE CWE

Triage CWE-636 against known exploitation evidence

Use CISA's Known Exploited Vulnerabilities catalog to test whether a vulnerability mapped to CWE-636, Not Failing Securely ('Failing Open'), 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-636

Apply MITRE's full root-cause mapping guidance when using CWE-636, Not Failing Securely ('Failing Open'). 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-636 with root-cause mapping checks

Apply MITRE's root-cause mapping quick tips to CWE-636, Not Failing Securely ('Failing Open'). 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-636: Not Failing Securely ('Failing Open')?+

CWE-636: Not Failing Securely ('Failing Open') is a Common Weakness Enumeration (CWE) entry maintained by MITRE. When the product encounters an error condition or failure, its design requires it to fall back to a state that is less secure than other options that are available, such as selecting the weakest encryption algorithm or using the most permissive access control restrictions. By entering a less secure state, the product inherits the weaknesses associated with that state, making it easier to compromise. At the least, it causes administrators to have a false sense of security. This weakness typically occurs as a result of wanting to "fail functional" to minimize administration and support costs, instead of "failing safe."

What are the security consequences of Not Failing Securely ('Failing Open')?+

If exploited, CWE-636 (Not Failing Securely ('Failing Open')) it can compromise Access Control, leading to outcomes such as Bypass Protection Mechanism.

How do you prevent or mitigate Not Failing Securely ('Failing Open')?+

Recommended mitigations for CWE-636 include: Subdivide and allocate resources and components so that a failure in one part does not affect the entire product.

Which programming languages are affected by Not Failing Securely ('Failing Open')?+

CWE-636 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 Not Failing Securely ('Failing Open')?+

MITRE documents real CVEs mapped to CWE-636, including CVE-2007-5277 and CVE-2006-4407. 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-636 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-636: Not Failing Securely ('Failing Open')

Extended Description

Technical Details

Applicable To

Security Consequences

Scope

Impact

Mitigation Strategies

Phase

Description

Detection Methods

Code Examples & CVEs

Observed CVE Examples (2)

CWE Relationships

Parent Weaknesses