The MCP Server Chose the Token Endpoint. Two Official SDKs Trusted It. — Cybersecurity Tech Brief By HackerNoon

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This story was originally published on HackerNoon at: https://hackernoon.com/the-mcp-server-chose-the-token-endpoint-two-official-sdks-trusted-it.
I found OAuth credential exposure flaws in the official MCP Python and TypeScript SDKs. Why patching CVE-2026-115563 and CVE-2026-104850 may not be enough.
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This story was written by: @aviralxroot. Learn more about this writer by checking @aviralxroot's about page, and for more stories, please visit hackernoon.com.

I reported two OAuth credential exposure flaws in the official MCP Python and TypeScript SDKs, now tracked as CVE-2026-115563 and CVE-2026-104850. A malicious MCP server could manipulate OAuth discovery, causing affected clients to send secrets, refresh tokens, or other credentials to attacker-controlled endpoints. Both SDKs have patches, but some integrations also need explicit issuer binding and updates to stored credentials.