GHSA-hjwh-xvfw-qrwj: Medium severity npm/mcp-searxng vulnerability

Summary

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

When the server starts in STDIO mode and an MCP client connects, the complete SEARXNGURL, 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: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:

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: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:

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.SEARXNGURL ): 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:password@searxng.example.com" } }, "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 SEARXNGURL invalid protocol for "${value}": ${url.protocol}; } } catch { return SEARXNGURL 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 SEARXNGURL as non-secret in .mcp/server.json:20-25:

json { "name": "SEARXNGURL", "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 SEARXNGURL='http://MCPPOCUSER7391:MCPPOCPASS7391@127.0.0.1:9' \ 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 \ 'MCPPOCUSER7391|MCPPOCPASS7391' \ credential-log-leak.txt

Observed result

The complete credential-bearing URL is exposed:

text SearXNG URLs: http://MCPPOCUSER7391:MCPPOCPASS7391@127.0.0.1:9

It is also delivered to the MCP client:

json { "method": "notifications/message", "params": { "level": "info", "data": { "message": "SearXNG URLs: http://MCPPOCUSER7391:MCPPOCPASS7391@127.0.0.1:9" } }, "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":"searxngwebsearch","arguments":{"query":"credential leak test"}}} EOF

Start the server with a credential-bearing URL that uses an unsupported protocol:

bash SEARXNGURL='ftp://MCPPOCUSER7391:MCPPOCPASS7391@example.invalid' \ timeout 8s node dist/cli.js \ < /tmp/mcp-error-poc.jsonl \ 2>&1 | tee credential-error-leak.txt

Search the response:

bash grep -nE \ 'MCPPOCUSER7391|MCPPOCPASS7391' \ credential-error-leak.txt

Observed result

The complete URL is exposed in the MCP logging notification:

text Tool execution error: Configuration Issues: SEARXNGURL invalid protocol for "ftp://MCPPOCUSER7391:MCPPOCPASS7391@example.invalid": ftp:

It is also returned directly in the JSON-RPC error:

json { "jsonrpc": "2.0", "id": 2, "error": { "code": -32603, "message": "Configuration Issues: SEARXNGURL invalid protocol for \"ftp://MCPPOCUSER7391:MCPPOCPASS7391@example.invalid\": 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 SEARXNGURL 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 SEARXNGURL entry has an unsupported protocol: ${url.protocol};

For malformed URLs:

typescript return "SEARXNGURL 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 SEARXNGURL 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