## FastMCP MCP client wrappers construct M2M OAuth providers without issuer binding — client secret redirectable to attacker-advertised authorization server

- 種別: advisory
- 重大度: medium
- 関連技術: python
- 公開日時: 2026-10-23T21:31:30.000Z
- 情報源: GitHub Advisory Database (https://github.com/advisories/GHSA-vqqp-x5qm-5qp4)
- パーマリンク: https://vulnpulse.app/items/ghsa-ghsa-vqqp-x5qm-5qp4

影響: pip:fastmcp >= 4.0.0a1, < 4.1.2 → 4.1.2, pip:fastmcp-slim >= 4.0.0a1, < 4.1.2 → 4.1.2
Maintainer assessment and remediation This report is accepted as a FastMCP credential-binding vulnerability. Affected versions of the OAuth client credentials providers do not expose the authorization-server issuer that owns pre-registered credentials. An untrusted or compromised MCP server can therefore advertise a different authorization server and receive the client secret or a signed assertion. Signing keys themselves remain local; assertion replayability depends on the assertion source and…