mongodb/node-mongodb-native · error · MongoRuntimeError

Server returned an invalid host

Error message

Server returned an invalid host: "${host}"

What it means

Thrown during MONGODB-AWS SASL exchange when the host returned by the server fails validation: length is 0, length exceeds 255, or it contains '..'. The host is used to build the STS GetCallerIdentity request URL, so an invalid value would enable host injection/path traversal and is rejected.

Solutions

1. Ensure you are connecting to a legitimate MongoDB server endpoint.
2. Remove intermediary proxies that could rewrite the response host field.
3. Report to the server vendor if the host field is unexpectedly malformed.

try {
  await client.connect();
} catch (e) {
  if (e instanceof MongoRuntimeError && /invalid host/.test(e.message)) {
    // inspect server endpoint / proxy; possible host injection
  }
  throw e;
}

When it happens

Trigger: serverResponse.h is empty, longer than 255 chars, or contains '..'. Fires at mongodb_aws.ts:95. Indicates a malformed server response or a malicious/buggy endpoint.

Common situations: A proxy injecting an unexpected host. A non-MongoDB endpoint responding to the saslStart command. Corrupted BSON.

Related errors

• Server nonce does not begin with client nonce
• Invalid server nonce length
• AuthContext must provide credentials.
• AWS_SESSION_TOKEN cannot be provided when using…
• Azure endpoint did not return a value with only…

AI-assisted analysis of mongodb/node-mongodb-native@dce7939f86 (2026-08-11). Data as JSON: /api/errors/8ca04947dd62c976. Report an issue: GitHub.

Appendix: source

Thrown at src/cmap/auth/mongodb_aws.ts:95

    };
    const host = serverResponse.h;
    const serverNonce = serverResponse.s.buffer;
    if (serverNonce.length !== 64) {
      // TODO(NODE-3483)
      throw new MongoRuntimeError(`Invalid server nonce length ${serverNonce.length}, expected 64`);
    }

    if (!ByteUtils.equals(serverNonce.subarray(0, nonce.byteLength), nonce)) {
      // throw because the serverNonce's leading 32 bytes must equal the client nonce's 32 bytes
      // https://github.com/mongodb/specifications/blob/master/source/auth/auth.md#conversation-5

      // TODO(NODE-3483)
      throw new MongoRuntimeError('Server nonce does not begin with client nonce');
    }

    if (host.length < 1 || host.length > 255 || host.indexOf('..') !== -1) {
      // TODO(NODE-3483)
      throw new MongoRuntimeError(`Server returned an invalid host: "${host}"`);
    }

    const body = 'Action=GetCallerIdentity&Version=2011-06-15';
    const headers = await aws4Sign(
      {
        method: 'POST',
        host,
        region: deriveRegion(serverResponse.h),
        service: 'sts',
        headers: {
          'Content-Type': 'application/x-www-form-urlencoded',
          'Content-Length': body.length,
          'X-MongoDB-Server-Nonce': ByteUtils.toBase64(serverNonce),
          'X-MongoDB-GS2-CB-Flag': 'n'
        },
        path: '/',
        body,
        date: new Date()

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