MCP OAuth Consent-Layer Confused Deputy via Open Dynamic Client Registration

mcp-oauth-consent-dcr-abuse is a high severity check in the ai category, written in python. Its source is templates/ai/mcp/mcp-oauth-consent-dcr-abuse.py in cert-x-gen-templates.

What it checks

ACTIVE check. Drives an MCP OAuth authorization server through open Dynamic Client Registration and observes, by behaviour, whether an attacker-registered redirect_uri receives an authorization code with NO re-consent - the consent-layer confused deputy. Distinct from token-audience and issuer-binding: this tests the consent + registration layer, not the token. Also checks RFC 9207 iss return and state binding.

There is a playbook for this check

MCP OAuth consent-layer confused deputy via open DCR sets out the use case, the probe flow, the oracle, and the fixture that proves it in both directions.

Header

Field	Value
Id	mcp-oauth-consent-dcr-abuse
Severity	high
Language	python
Category	ai
Author	Bugb Research
Template version	1.0.0
Confidence	90
CVSS	8.2
Weakness	CWE-441, CWE-601
Tags	mcp, ai, agent, oauth, oauth-conformance, dynamic-client-registration, dcr, consent, confused-deputy, redirect-uri, rfc9207, rfc7591, authorization-server, behavioural, active, intrusive, cwe-441, cwe-601
Target kind	http
Oracle	property

Conventions of the repository, not fields the engine reads

@target_kinds and @oracles are documented in the templates repository’s contribution guide, and cxg’s annotation parser does not carry them into a template’s metadata. Nothing at scan time selects on them. The annotation header schema is every field the parser does read.

References

Declared in the header. cxg parses @references and then discards it, and nothing at scan time reads it, so this is the only place the links a template cites are surfaced.

• https://modelcontextprotocol.io/specification/2026-07-28/basic/authorization
• https://modelcontextprotocol.io/specification/2026-07-28/basic/authorization/client-registration
• https://modelcontextprotocol.io/specification/2026-07-28/basic/authorization/security-considerations
• https://www.rfc-editor.org/rfc/rfc7591.html
• https://www.rfc-editor.org/rfc/rfc9207.html
• https://www.rfc-editor.org/rfc/rfc6749.html#section-10.6
• https://cwe.mitre.org/data/definitions/441.html
• https://cwe.mitre.org/data/definitions/601.html

Run it

To see what the copy on your machine says about itself, and to confirm it is installed at all:

cxg template info mcp-oauth-consent-dcr-abuse

The id it prints is the one to pass anywhere a template is selected. See cxg template for the rest of the subcommand, Scan a target for running a scan, and A match is not a finding for how to read what comes back.

Related

• Template catalog is the whole corpus.
• ai is the rest of this category.
• Templates by weakness class groups checks by the defect they look for.
• Contribute a template is the route from a check you needed and could not find to a merged one.