MCPP-PRM06: Bearer tokens accepted in the query string

Family	Protected Resource Metadata (RFC 9728)
Default severity	high
Confidence	high
Mode	passive (default scan)
Spec revisions	2025-06-18 and later

Why it matters

Tokens in URLs leak into logs, proxies and Referer headers. OAuth 2.1 and the MCP spec forbid them; RFC 6750 §2.3 says the method SHOULD NOT be used.

Remediation

Remove query from bearer_methods_supported and ignore access_token query parameters on the resource server.

References

• RFC 6750 Bearer Token Usage
• OAuth 2.1 (draft-ietf-oauth-v2-1-16)
• MCP 2025-03-26 Authorization

Suppressing

# .mcp-posture-ignore
[[ignore]]
check = "MCPP-PRM06"
target = "https://mcp.example.com/*"
justification = "Why this is acceptable here"
expires = 2026-12-31