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CVE-2026-59971 – Unauthenticated Remote SQL Execution (RCE) – MySQL MCP Server < 0.4.2

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Summary

CVE-2026-59971 is a critical missing-authentication / origin-validation vulnerability affecting the mysql_mcp_server package (designcomputer) when run in SSE/HTTP transport mode. Versions prior to 0.4.2 fail to enforce DNS-rebinding protection, CORS restrictions, or any authentication on the server’s /, /sse, and /messages/ endpoints, allowing a remote, unauthenticated attacker to execute arbitrary SQL queries against the backend MySQL database. The issue carries the maximum CVSS v3.1 score of 10.0 (Critical) due to full compromise of confidentiality, integrity, and availability with no privileges or user interaction required.

Technical details

  • Root cause: When started with SSE/HTTP transport, the server constructs the MCP SDK’s SseServerTransport without supplying security_settings, which leaves the SDK’s built-in DNS-rebinding protection (enable_dns_rebinding_protection) disabled by default. The underlying Starlette application also lacks CORS and TrustedHost middleware, and none of its routes require credentials.
  • Trigger conditions: The vulnerability only manifests when the server is launched with MCP_TRANSPORT=sse; the default stdio transport mode is not affected. The service also binds to 0.0.0.0 by default, exposing it on all network interfaces.
  • Attack vector: Network (AV:N), no privileges or user interaction required. An attacker can either (a) directly reach an exposed /sse or /messages/ endpoint over the network, or (b) use DNS rebinding to redirect a victim browser’s requests to a locally-bound instance, bypassing same-origin protections.
  • Impact: Once reachable, an attacker can invoke the server’s execute_sql tool to run arbitrary SQL commands without any credentials. This enables full database read/write access and, where the connected MySQL account holds FILE privileges, can be escalated to arbitrary file read/write and remote code execution on the host.

Affected software

  • mysql_mcp_server (designcomputer) — all versions prior to 0.4.2, when configured with MCP_TRANSPORT=sse

Severity

  • CVSS v3.1 Base Score: 10.0 (Critical)
  • Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

Mitigation and recommended actions

  • Immediate: Upgrade mysql_mcp_server to version 0.4.2 or later, which enables DNS-rebinding protection (TransportSecuritySettings(enable_dns_rebinding_protection=True)) and no longer defaults to an unauthenticated, unrestricted binding.
  • If immediate patching is not possible:
    • Avoid running the server with MCP_TRANSPORT=sse until patched; use the default stdio transport where feasible.
    • Bind the service to 127.0.0.1 rather than 0.0.0.0 to prevent direct network exposure.
    • Place any SSE/HTTP-mode instance behind a reverse proxy or firewall that enforces authentication and restricts access to trusted hosts/origins only.
    • Restrict the MySQL account used by the server to the minimum required privileges, and explicitly revoke FILE privileges to reduce the risk of RCE via file operations.

References

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