CVE-2026-104850: MCP TypeScript SDK: OAuth client could send credentials to an authorization server chosen by the MCP server

What it is

In affected versions, the SDK's OAuth client let the MCP server decide which authorization server received the client's OAuth credentials. Credentials were not tied to the authorization server they belong to.

A malicious or compromised MCP server could name its own authorization server. With no user interaction, the client would send it:

- the refresh_token and client_secret stored from an earlier sign-in - the client_secret or signed assertion configured on a bundled provider

How to check

1. Affected: @modelcontextprotocol/sdk (npm) >= 1.12.0, < 1.31.0.
2. Affected: @modelcontextprotocol/client (npm) >= 2.0.0, < 2.2.0.
3. Compare your installed version with the range above (command below).

How to fix

1. Upgrade @modelcontextprotocol/sdk to 1.31.0 or later.
2. Upgrade @modelcontextprotocol/client to 2.2.0 or later.

npm ls @modelcontextprotocol/sdk
npm ls @modelcontextprotocol/client

Sources

• GitHub Security Advisory GHSA-6qxp-vccf-f47h ↗
• NVD: CVE-2026-104850 ↗