Vulnerability in MCP Protocol Software Development Kit Threatens OAuth Credentials

The maintenance team of the official Python software development kit for the Model Context Protocol revealed a vulnerability that allows malicious servers to steal OAuth credentials, including client secrets, authorization codes and PKCE proof keys, by directing the client to an attacker-controlled endpoint. Cycode, which reported the flaw, proved an attacker can use the stolen data to request a valid access token carrying all the permissions granted to the application. Affected versions include 1.9.1 through 1.29.1 in the first series and 2.0.0 through 2.1.1 in the second, fixed in versions 1.30.0 and 2.2.0 respectively, with administrators urged to upgrade, rotate client secrets and revoke suspicious tokens.