Developer Rejects Security Advice on OAuth Endpoint, Finds Real Flaw Elsewhere

A developer running a QR code service received an unsolicited security report last week flagging an open OAuth dynamic client registration endpoint as a vulnerability. The developer argued the endpoint was functioning as intended, since the Model Context Protocol requires open dynamic registration to allow AI clients like Claude to connect without prior approval. The suggested fixes — requiring access tokens or a redirect URI allowlist — would have effectively disabled MCP support, and the redirect concern was already mitigated by strict per-client checks enforced at both authorization and token exchange. However, investigating the report led the developer to spot a genuine risk: the consent screen displayed the attacker-controlled 'client_name' field as trusted text, enabling anyone to register a client named something like 'QRFLOW Official Support' and craft a convincing phishing page on the real domain. The actual fix addressed how unverified client names were rendered on the consent screen, leaving the registration endpoint itself untouched.