SearXNG Basic Authentication Credentials Exposed Through MCP Logs and JSON-RPC Error Responses

Summary

mcp-searxng version 1.11.0 exposes SearXNG Basic Authentication credentials embedded in the SEARXNG_URL environment variable.

When the server starts in STDIO mode and an MCP client connects, the complete SEARXNG_URL, including its username and password, is sent to the client through an MCP notifications/message logging notification.

Additionally, when URL validation fails, the complete credential-bearing URL is included in the configuration error. This error is logged through MCP and returned to the client as a JSON-RPC error response.

For example, a value such as:

http://username:password@searxng.example.com

is exposed without redaction.

A connected MCP client or anyone with access to captured server logs may recover the SearXNG credentials and use them to access the configured SearXNG instance.

The issue was confirmed in:

mcp-searxng 1.11.0

Suggested severity: Medium

Details

mcp-searxng supports SearXNG Basic Authentication by embedding credentials in the URL userinfo component:

https://username:password@searxng.example.com

The project contains a redaction function named redactSearxngInstanceUrl(), but it is not used in several logging and error-handling paths.

Startup console disclosure

In src/index.ts:373-378, the server retrieves the raw SearXNG URLs and writes them directly to stderr:

const searxngInstances = getSearxngInstances();

if (searxngInstances.length > 0) {
  console.error(`🌐 SearXNG URLs: ${searxngInstances.join("; ")}`);
}