OFFICIAL MCP PYTHON SDK FLAW CAN LET MALICIOUS SERVERS STEAL OAUTH CREDENTIALS

Summary from the TLDR InfoSec newsletter

A high-severity flaw in the official MCP Python SDK let malicious MCP servers redirect OAuth token requests to attacker-controlled endpoints. Affected 1.x (1.9.1–1.29.1) and 2.x (2.0.0–2.1.1) clients sent the client secret, authorization code, and PKCE proof key to the attacker, enabling full account takeover with the app's granted permissions. Fixes are in 1.30.0 and 2.2.0. ClientCredentialsOAuthProvider and PrivateKeyJWTOAuthProvider also require passing issuer= to pin the expected login service.