Insecure Caching of MCP Response

Description

An MCP server was found to use a public cache scope with a short time-to-live (TTL) for responses to methods such as tool listing and resource listing. A public cache scope may allow responses to be cached and reused without being restricted to a particular client or user context. Although a short TTL limits how long cached responses remain valid, it does not by itself ensure that public caching is appropriate. Depending on the response contents and server behavior, shared caching may expose information about available tools or resources or return cached results that are not appropriate for the requesting client.

Recommendation

Review the MCP server response-caching configuration and determine whether public caching is appropriate for the methods being cached. Use a public cache scope only when responses are suitable for sharing across clients and do not depend on client identity, session state, or authorization context. Where responses may differ by client or access permissions, use an appropriate private or isolated cache scope, or disable caching. Configure TTL values and cache invalidation according to the sensitivity and expected freshness of the responses. Test methods such as tool listing and resource listing to verify that cached responses cannot be incorrectly reused across authorization contexts.

References

• Model Context Protocol: Security Best Practices
• OWASP Web Security Testing Guide