# MCP Python SDK flaw could expose login credentials to malicious servers

_Published Tuesday, September 29, 2026 at 4:06 AM EDT · Security, Infrastructure · Latest · Tier 2 — Notable_

![MCP Python SDK flaw could expose login credentials to malicious servers — Primary](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh2N5owhsoQXHTQV74afwfngdyitjwcW37BHLX2QKkq6xZAxP8_AOXAh1ODPj5DyvvmMUq3mKH9eR2B1r7owc6djzLViK2U4BY_hw3rTWmaHjhFEyyh8LPlUMPZ7MdWkqN7bjtQyMByBLrsI5m0mAU9y-IbrsAe9OPhZXHN63AWwuv_1OB5MSrpRdVZ9CM/s1700-nu-rw-lo-l85-e365/mcp-python.jpg)

A security advisory disclosed on September 28 says a malicious server could cause applications using affected versions of the official MCP Python SDK to send OAuth login credentials to an attacker. The flaw affects certain applications that use the SDK as an HTTP client to connect to servers they do not fully control. Security firm Cycode demonstrated that the stolen credentials could be exchanged for an access token.

Fixes are available in versions 1.30.0 and 2.2.0. For two affected providers, users must also set `issuer=` to identify the intended login service; upgrading alone does not close that route. The advisory and Cycode reported no attacks using the flaw.

## Sources

- [The Hacker News](https://thehackernews.com/2026/09/official-mcp-python-sdk-flaw-can-let.html)

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Canonical: https://techandbusiness.org/newswire/0MK3Lp4Q9cBOcKT66AidYi
Published: 2026-09-29T08:06:44.445Z
Story chronology: 2026-09-28T00:00:00.000Z
Retrieved: 2026-09-29T10:15:42.699Z
Publisher: Tech & Business (techandbusiness.org)