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app.use((err, req, res, next) => {
    console.error(err.stack);
    res.status(500).send('Something broke!');
});

The provided error handling code in the Express.js application adheres to some security best practices but can be improved in the following ways:

1. **Information Disclosure**: The use of `err.stack` in `console.error` is standard for logging errors; however, ensure that such detailed error information is not exposed to the client. Detailed stack traces can provide attackers with insights into the underlying architecture and potential vulnerabilities.

2. **Generic Error Messages**: The code correctly sends a generic error message (`'Something broke!'`) to the client, which is a good practice to avoid information leakage. However, it could be enhanced by providing slightly more context to help the end-user understand what action to take next, without revealing sensitive details.

3. **Error Handling Granularity**: The error handler does not differentiate between different types of errors. Implementing more granular error handling, such as distinguishing between 4xx and 5xx status codes, can improve client-side error resolution and system diagnostics without compromising security.

4. **Logging and Monitoring**: Ensure that all errors, especially runtime exceptions, are logged to a secure, external logging service or a file with restricted access. This assists in monitoring and investigating incidents without exposing sensitive information to users.

5. **Rate Limiting and Monitoring**: Consider implementing rate limiting for error responses to prevent error-based attack tactics like forced browsing. Additionally, monitor error rates to detect and respond to potential attacks.

6. **HTTP Headers**: Ensure that appropriate HTTP headers are set in the error response to prevent caching of error pages and mitigate against clickjacking or other client-side attacks.

Here is a revised version of the error handling code considering these recommendations:

```javascript
app.use((err, req, res, next) => {
    console.error(err.stack);  // Log the error internally

    // Differentiate between client-side and server-side errors
    const statusCode = err.status ? err.status : 500;
    const errorMessage = statusCode === 500 ? 'Internal Server Error' : err.message;

    // Set no-cache headers
    res.set('Cache-Control', 'no-store');
    res.set('X-Frame-Options', 'DENY');

    // Send the generic or specific error message
    res.status(statusCode).send(errorMessage);
});