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

Summary

### 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: ```text http://username:[email protected] ``` 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: ```text mcp-searxng 1.11.0 ``` Suggested severity: **Medium** ### Details mcp-searxng supports SearXNG Basic Authentication by embedding credentials in the URL userinfo component: ```text https://username:[email protected] ``` 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: ```typescript const searxngInstances = getSearxngInstances(); if (searxngInstances.length > 0) { console.error(`🌐 SearXNG URLs: ${searxngInstances.join("; ")}`); } ``` `getSearxngInstances()` returns the unmodified environment-variable values. Relevant code in `src/searxng-instances.ts:25-38`: ```typescript export function parseSearxngUrls( raw: string | undefined = process.env.SEARXNG_URL ): string[] { if (raw === undefined) { return []; } return raw .split(";") .map((entry) => entry.trim()) .filter((entry) => entry !== ""); } export function getSearxngInstances(): string[] { return parseSearxngUrls(); } ``` #### MCP logging notification disclosure After the MCP client connects, `src/index.ts:388-393` sends the complete URL through the MCP logging interface: ```typescript const searxngInstances = getSearxngInstances(); logMessage( mcpServer, "info", `SearXNG URLs: ${ searxngInstances.length > 0 ? searxngInstances.join("; ") : "not configured" }` ); ``` `logMessage()` passes this value to `sendLoggingMessage()` in `src/logging.ts:15-25`: ```typescript mcpServer.sendLoggingMessage({ level, data: notificationData }); ``` As a result, the connected MCP client receives a message containing the username and password: ```json { "method": "notifications/message", "params": { "level": "info", "data": { "message": "SearXNG URLs: http://username:[email protected]" } }, "jsonrpc": "2.0" } ``` #### Configuration error disclosure The URL validation function includes the complete unredacted value in error messages. Relevant code in `src/searxng-instances.ts:44-52`: ```typescript export function validateSearxngInstanceUrl( value: string ): string | null { try { const url = new URL(value); if (!["http:", "https:"].includes(url.protocol)) { return `SEARXNG_URL invalid protocol for "${value}": ${url.protocol}`; } } catch { return `SEARXNG_URL invalid format: ${value}`; } return null; } ``` The validation error is aggregated by `validateEnvironment()` in `src/error-handler.ts:175-203`: ```typescript const validationError = validateSearxngInstanceUrl(searxngUrl); if (validationError) { issues.push(validationError); } ``` The complete error is then thrown from `src/search.ts:689-693`: ```typescript const validationError = validateEnvironment(); if (validationError) { logMessage(mcpServer, "error", "Configuration invalid"); throw new MCPSearXNGError(validationError); } ``` The tool handler in `src/index.ts:254-260` sends the error message and stack trace through MCP logging, then rethrows it: ```typescript logMessage( mcpServer, "error", `Tool execution error: ${ error instanceof Error ? error.message : String(error) }`, { tool: name, args: args, error: error instanceof Error ? error.stack : String(error) } ); throw error; ``` Rethrowing the error causes the same unredacted credential-bearing URL to be returned in the JSON-RPC error response. #### Existing redaction function is not used The project already contains a suitable redaction function in `src/searxng-instances.ts:57-69`: ```typescript export function redactSearxngInstanceUrl( raw: string ): string { try { const url = new URL(raw); if (!url.username && !url.password) { return raw; } url.username = ""; url.password = ""; return url.toString(); } catch { return raw.replace( /^([a-zA-Z][a-zA-Z0-9+.-]*:\/\/)[^/]*@/, "$1" ); } } ``` However, this function is not applied before startup logging, MCP logging, or configuration error construction. The MCP manifest also marks `SEARXNG_URL` as non-secret in `.mcp/server.json:20-25`: ```json { "name": "SEARXNG_URL", "description": "URL of your SearXNG instance", "isRequired": true, "isSecret": false, "format": "string" } ``` Because credentials may be embedded in this variable, it should be classified as a secret. ### PoC The following proof of concept uses fake credentials. A real SearXNG server is not required. #### Requirements ```text Node.js 20 or newer npm mcp-searxng 1.11.0 source code ``` #### Build the application ```bash unzip mcp-searxng-main.zip cd mcp-searxng-main npm ci npm run build ``` #### Test 1: Credential disclosure through MCP logging Create an MCP initialization request: ```bash cat > /tmp/mcp-init.jsonl <<'EOF' {"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2024-11-05","capabilities":{},"clientInfo":{"name":"credential-leak-poc","version":"1.0.0"}}} EOF ``` Start the server with fake credentials embedded in a valid HTTP URL: ```bash SEARXNG_URL='http://MCP_POC_USER_7391:[email protected]:9' \ timeout 8s node dist/cli.js \ < /tmp/mcp-init.jsonl \ 2>&1 | tee credential-log-leak.txt ``` Search the output for the credentials: ```bash grep -nE \ 'MCP_POC_USER_7391|MCP_POC_PASS_7391' \ credential-log-leak.txt ``` #### Observed result The complete credential-bearing URL is exposed: ```text SearXNG URLs: http://MCP_POC_USER_7391:[email protected]:9 ``` It is also delivered to the MCP client: ```json { "method": "notifications/message", "params": { "level": "info", "data": { "message": "SearXNG URLs: http://MCP_POC_USER_7391:[email protected]:9" } }, "jsonrpc": "2.0" } ``` This confirms that a connected MCP client can recover the configured username and password without accessing the host environment. #### Test 2: Credential disclosure through JSON-RPC errors Create initialization and tool-call requests: ```bash cat > /tmp/mcp-error-poc.jsonl <<'EOF' {"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2024-11-05","capabilities":{},"clientInfo":{"name":"credential-error-poc","version":"1.0.0"}}} {"jsonrpc":"2.0","id":2,"method":"tools/call","params":{"name":"searxng_web_search","arguments":{"query":"credential leak test"}}} EOF ``` Start the server with a credential-bearing URL that uses an unsupported protocol: ```bash SEARXNG_URL='ftp://MCP_POC_USER_7391:[email protected]' \ timeout 8s node dist/cli.js \ < /tmp/mcp-error-poc.jsonl \ 2>&1 | tee credential-error-leak.txt ``` Search the response: ```bash grep -nE \ 'MCP_POC_USER_7391|MCP_POC_PASS_7391' \ credential-error-leak.txt ``` #### Observed result The complete URL is exposed in the MCP logging notification: ```text Tool execution error: Configuration Issues: SEARXNG_URL invalid protocol for "ftp://MCP_POC_USER_7391:[email protected]": ftp: ``` It is also returned directly in the JSON-RPC error: ```json { "jsonrpc": "2.0", "id": 2, "error": { "code": -32603, "message": "Configuration Issues: SEARXNG_URL invalid protocol for \"ftp://MCP_POC_USER_7391:[email protected]\": ftp:" } } ``` The raw username and password are therefore exposed through both logging and protocol responses. ### Impact This is a sensitive credential disclosure vulnerability. The following parties may obtain the credentials: 1. A connected MCP client receiving logging notifications. 2. A client capable of invoking a tool and receiving JSON-RPC errors. 3. A user or process with access to captured stderr output. 4. A centralized logging or monitoring system collecting application logs. 5. Other users with access to shared log files or container logs. The exposed credentials may allow an attacker to authenticate directly to the configured SearXNG instance. Depending on the SearXNG deployment and the permissions associated with the account, this may allow: 1. Unauthorized use of a private SearXNG service. 2. Access to functionality restricted through Basic Authentication. 3. Consumption of private server resources. 4. Exposure of information available only to authenticated users. 5. Further account compromise where the credentials have been reused. The default STDIO transport limits the exposure to the connected parent MCP client and local logging environment. However, MCP clients should not receive upstream service credentials, and the project security documentation explicitly treats credentials embedded in `SEARXNG_URL` as secrets that must be redacted. ### Suggested mitigation Apply `redactSearxngInstanceUrl()` before including any SearXNG URL in console or MCP logging: ```typescript const redactedInstances = getSearxngInstances() .map(redactSearxngInstanceUrl); logMessage( mcpServer, "info", `SearXNG URLs: ${ redactedInstances.length > 0 ? redactedInstances.join("; ") : "not configured" }` ); ``` Do not include raw configuration values in validation errors. A generic error can be returned instead: ```typescript return `SEARXNG_URL entry has an unsupported protocol: ${url.protocol}`; ``` For malformed URLs: ```typescript return "SEARXNG_URL contains an invalid URL"; ``` The following additional changes are recommended: 1. Redact URLs before writing them to stderr. 2. Redact secrets before sending MCP logging notifications. 3. Avoid including raw environment-variable values in exceptions. 4. Avoid returning detailed stack traces containing secrets to MCP clients. 5. Mark `SEARXNG_URL` as secret in `.mcp/server.json`: ```json "isSecret": true ``` 6. Add regression tests that assert usernames and passwords never appear in: * stderr output * MCP logging notifications * JSON-RPC error responses * stack traces * configuration resources