How to meet it
OWASP AISVS v1.01
Model Context Protocol (MCP) Security · Schema, Message, and Input Validation
Reject schemas with unresolved references
Verify that MCP implementations reject schemas that fail to validate due to an unresolved external `$ref` rather than treating them as permissive.
OWASP AISVS v1.01, requirement 10.4.15
In plain English
If a schema cannot be checked because an external reference did not resolve, reject it. Treating it as "anything goes" opens a gap.
What good looks like
- Unresolved references cause validation to fail.
- Failures are logged.
- Tests cover unresolved references.
How teams usually do it
- Strict mode in the validation library.
Evidence an auditor would accept
- Tests showing rejection.
Common mistakes
- Libraries that treat unknown references as an empty, permissive schema.
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Requirement text from the OWASP AI Security Verification Standard, licensed under CC BY-SA 4.0. This guidance is shared under the same licence.