What is a 401 Error and How do You Fix it?

We’ve all been there at least once: logging in and entering the wrong credentials on a website.  

It’s like trying to unlock your front door with the wrong key. The key won’t unlock and let you in. That’s what a 401 error is—the return error when accessing anything online without the proper credentials.  

This article will explain what causes 401 errors, besides the incorrect login details, and how to fix them. So, let’s get started! 

What is a 401 error?  

A 401 error is an HTTP status code that a server returns when a user incorrectly enters their website credentials.  

It’s important to note that a 401 error is different from other related errors, such as:  

• 403 Forbidden. This error occurs when you’re authenticated but don’t have permissions to access the resource.  

• 404 Not Found. This happens when the requested resource doesn’t exist on the server.  

When you encounter a 401 error, you’ll typically see a message like “You are not authorized to view this page” or “Authentication required.”  

While the exact wording may vary depending on the website or application, the underlying meaning remains the same. You need to provide valid credentials to proceed.  

Common causes of the 401 error  

It’s easy to feel frustrated when you encounter a 401 error. But let’s look at why it happens below. 

Incorrect credentials   

One of the most common reasons for encountering a 401 error is entering the wrong username or password. This can happen due to a simple typo, a case-sensitivity mismatch, or using an outdated password. When the credentials you provide don’t match what the server expects, it will return a 401 error.  

Session expiration   

A session is a temporary “record” created by a website or app to remember who you are after you log in. It stores your authentication details (like your username and password), so you don’t have to log in again while browsing.  

However, sessions don’t last forever. If you remain inactive for too long or don’t make any requests before the session times out, the server will no longer recognize your login. This results in a 401 error, meaning you need to log in again to continue.  

Misconfigured permissions  

Sometimes, the 401 error can occur due to incorrectly set permissions on the server side. If the server is configured to restrict access to a resource, even for authenticated users, it will return a 401 error.  

Missing authentication token   

In the context of APIs and web services, authentication often involves tokens rather than traditional username-password combinations. An API (Application Programming Interface) is a set of rules that allows different software applications to communicate with each other. It acts as a bridge between different systems.  

When you make an API request, authentication token should be included in the request header to prove that you have permission to access the requested resource.  If you make a request to an API endpoint without including the required authentication token, you’ll receive a 401 error.  

Server-side restrictions   

Servers may implement various security measures that can trigger a 401 error. Servers with IP-based restrictions will return a 401 error if your IP address isn’t whitelisted, even with correct login credentials. Many servers also use rate limiting to temporarily block access when you exceed the allowed number of requests within a timeframe.  Without completing these extra verification steps, the server will respond with a 401 error to protect sensitive resources from unauthorized access. 

Types of 401 error codes 

The 401 Unauthorized error can have different subcodes, each pointing to a specific cause. Here are the most common types. 

• 401.1 – Failed login attempt. This error occurs when a user submits incorrect login credentials during an authentication process. The server compares the provided username and password against its records and, if there’s a mismatch, server returns a 401.1 error. Common scenarios include typos in the password field or attempting to access an account without proper permission. 

• 401.2 – Server configuration caused the failed login attempt. A 401.2 error indicates that the server’s authentication settings are misconfigured. This can stem from issues like incorrect authentication protocol setup, missing or expired SSL/TLS certificates, or improperly configured access control rules. For instance, if an administrator updates the server’s authentication method without thoroughly testing it, users may face this error during login attempts. 

• 401.3 – ACL (Access Control List) caused the failed login attempt. Access Control Lists (ACLs) regulate users for specific resources. If a user tries to access a resource that they’re not allowed, the server sends a 401.3 error. This scenario is common in systems with role-based access control, such as when a regular user attempts to access admin-only feature or a restricted area of the application. 

• 401.501 – Client generated too many requests. Servers impose rate limits on client requests to protect server resources. If a client sends too many requests within a short time frame the server responds with a 401.501 error. This can happen when a client application has a bug causing it to send excessive requests or if a malicious user attempts a denial-of-service (DoS) attack. 

• 401.502 – Client reached dynamic IP restriction limit. Servers employ dynamic restrictions or blocks on IP addresses exhibiting suspicious behavior, such as sending a high volume of requests or attempting to access forbidden resources. When a client from a restricted IP sends a request, the server replies with a 401.502 error. This situation arises when an IP is flagged due to prior malicious activity or if an attacker uses the IP for brute-force attempts. 

• 401.503 – Client’s IP is in the server’s deny list. Server administrators can add problematic IP addresses to a deny list (a list of IP addresses that are suspected to be sources of malicious activity). If a client’s IP is on this list and they try to access the server, they’ll receive a 401.503 error. This often happens when an IP is identified as a source of spam, hacking attempts, or other malicious activities. 

• 401.504 – Client’s hostname is in the server’s deny list. Similar to IP deny lists, servers can also block requests from specific hostnames. If a client’s hostname is on the server’s deny list, any attempt to access the server will result in a 401.504 error. This can occur if a domain is known to host malware, engage in phishing, or consistently send spam requests. 

How to fix a 401 error: 9 different ways  

1. Clear browser cache and cookies   

When you encounter a 401 error, one of the first things to try is clearing your browser’s cache and cookies. You can also perform a hard refresh, which forces your browser to reload the page from the server instead of using cached data. To do a hard refresh, press Ctrl + F5 or Ctrl + Shift + R (Windows) or Cmd + Shift + R (Mac).  

Here’s how to clear cache and cookies in popular browsers:  

• Chrome. Click the three-dot menu, go to Clear browsing data, select Cookies and other site data and Cached images and files, then click Clear data.  

• Firefox. Click the hamburger menu, select Options > Privacy & Security, scroll down to Cookies and Site Data, and click Clear Data.  

• Safari. Click Safari > Preferences > Privacy, then click Manage Website Data and Remove All.  

• Edge. Click the three-dot menu, select Settings > Privacy, search, and services, under Clear browsing data, click Choose what to clear, select Cookies and other site data and Cached images and files, then click Clear now.  

2. Check credentials   

Double-check that you’re using the correct username and password. If you’re unsure, try resetting your password or contacting the website or application’s support team for assistance.  

3. Check URL and login paths   

Ensure you’re accessing the correct URL, and the login path hasn’t changed. A simple typo in the URL or a recent update to the login process could trigger a 401 error.  

4. Review server-side settings   

If you have access to the server configuration files, such as .htaccess for Apache or nginx.conf for NGINX, review the authentication settings to make sure they’re properly configured and not causing the 401 error.  

5. Examine authentication tokens  

For API requests, inspect the headers to ensure that the authentication token is correctly added. If the token is missing or invalid, generate a new one or check the API documentation for the proper authentication.  

6. Disable plugins or themes (WordPress)  

If you’re encountering a 401 error on a WordPress site, try deactivating plugins one by one to identify if a specific plugin is causing the issue. Go to your WordPress dashboard, look for Plugins > Installed Plugins, and click Deactivate for each plugin. If the error persists, try switching to a default theme to rule out theme-related issues.  

7. Flush DNS cache   

Flushing your DNS cache is different from clearing your browser cache or performing a hard refresh. While clearing browser cache and hard refresh deal with data stored in your browser, flushing DNS cache clears the stored IP addresses and other DNS records on your device or system.  

Flushing the DNS cache can help resolve 401 errors caused by outdated DNS records, which can direct your requests to the wrong server or resource.   

Here’s how to flush the DNS cache on different platforms:  

• Windows. Open Command Prompt and type ipconfig /flushdns.  

• Mac. Open Terminal and type sudo dscacheutil -flushcache.  

• Linux. Open Terminal and type sudo systemd-resolve –flush-caches.  

8. Check WWW-Authenticate header  

The WWW-Authenticate header provides information about which server supports authentication schemes. Developers can inspect the headers and determine the specific authentication method (e.g., basic authentication, digest authentication, or OAuth) to access the resource, which is crucial information for implementing the correct authentication mechanism in applications.  

9. Review server logs (for admins)    

If you’re a server administrator, check error logs to pinpoint authentication issues and fix any server-side problems. Common fixes include updating permission settings, correcting authentication configurations, or resolving IP whitelisting issues. 

How to prevent 401 errors  

While fixing 401 errors is important, it’s even better to prevent them from happening in the first place. Here are the best practices to minimize the occurrence of 401 errors.  

Use secure authentication   

Implement strong authentication methods, such as multi-factor authentication (MFA) or two-factor authentication (2FA), to protect user accounts and reduce the risk of unauthorized access. These methods add an extra layer of security by requiring users to provide additional proof of identity, such as a code sent to their phone or email, before granting access.  

Monitor session expiration   

Keep an eye on session timeouts and consider extending them if users frequently encounter 401 errors as a result. You can also implement session management techniques, such as idle timeouts or automatic session renewal, to ensure that users remain authenticated while actively using the application or website.  

Implement proper permission management   

Manage permissions tightly. Review user access regularly and limit permissions to only what’s needed. This prevents unauthorized access and reduces 401 errors.   

Regularly update credentials   

Encourage users to change their passwords periodically and educate them on the importance of using strong, unique passwords for each account. Implement password policies that require regular updates and prevent using weak or easily guessable passwords. This can help reduce the risk of unauthorized access and associated 401 errors.  

401 error in development: What developers need to know  

Understanding the 401 error is crucial for developers building secure and robust applications. Here are key points to keep in mind:  

API authentication  

When working with APIs, carefully review the authentication requirements in the API documentation. Make sure your application includes the necessary authentication tokens or credentials in each request header. Missing or invalid tokens commonly cause 401 errors in API integrations.  

HTTP headers  

Understand the role of the WWW-Authenticate header sent by the server in response to a 401 error. This header provides details about the authentication scheme and any additional parameters required for successful authentication. Knowing how to interpret and respond to this header is essential for proper implementation.  

Error handling  

Design your application to handle 401 errors smoothly, providing clear, user-friendly messages to guide users through the authentication process. When a 401 error occurs, prompt users to re-authenticate and offer helpful instructions for resolving the issue. Effective error handling reduces user frustration and improves the overall experience.  

Resolve 401 errors for seamless browsing  

Understanding the causes, troubleshooting techniques, and best practices can reduce the impact of 401 errors and ensure a smoother, more secure experience for both users and developers 

If you find this article helpful, explore our other resources to expand your knowledge. We provide you with the knowledge and tools you need to succeed online. If you’re looking for expert guidance on optimizing your website’s security and authentication, our team is here to help.  

Reach out today to learn more about how we can support your online goals. 

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