CVE-2026-104850: MCP TypeScript SDK: OAuth client could send credentials to an authorization server chosen by the MCP server
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_tokenandclient_secretstored from an earlier sign-in - the
client_secretor signed assertion configured on a bundled provider
References
- github.com/advisories/GHSA-6qxp-vccf-f47h
- github.com/modelcontextprotocol/typescript-sdk/commit/edd12e282620ebf770d67316f19cf91d4112a1bd
- github.com/modelcontextprotocol/typescript-sdk/pull/2887
- github.com/modelcontextprotocol/typescript-sdk/releases/tag/v2.2.0
- github.com/modelcontextprotocol/typescript-sdk/security/advisories/GHSA-6qxp-vccf-f47h
- nvd.nist.gov/vuln/detail/CVE-2026-104850
Code Behaviors & Features
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