API Failure: 7 Causes and How to Fix Them

APIs have revolutionized how web and web app developers interact with data, whether for personal use or business. One of our most profound responsibilities as API developers is to protect our endpoints from being hacked. Even with essential safeguards in place, our websites can be vulnerable. This post discusses seven causes of API failures and how to fix them. 

What Is an API Failure?

An API failure is any response that doesn’t conform to the system’s expected behavior being invoked by the client. One example is when a client makes a request to an API that is supposed to return a list of users but returns an empty list (i.e., {}). A successful response must have a status code in the 200 series. An unsuccessful response must have either an HTTP error code or a 0 return value. 

What Are the Common API Error Codes?

An API will raise an exception if it can’t process a client request correctly. The following are the common error codes and their meanings: 

  • 400 Bad Request: This error occurs when the client request is malformed or cannot be processed by your API.
  • 401 Unauthorized: This error occurs when an API key is missing or incorrectly entered.
  • 403 Forbidden: This error occurs when a user tries to access a resource they don’t have permission to see.
  • 404 Not Found: This error, also known as a File Not Found error, rarely has anything to do with the API itself but instead with the underlying system (for example, if trying to access a file that doesn’t exist on the server). This is usually related to something else and not directly related to your API code.
  • 500 Internal Server: This error occurs when your server can’t respond to a request from a user or can’t find some data (for example, you’re trying to access any post, but none of the posts exist for the given ID). 


What Causes API Failure?

An API failure can happen because of issues with the endpoints like network connectivity, latency, and load balancing issues. The examples below may give you a good understanding of what causes an API failure. 

1. Incorrect API Permissions

Some APIs are better left locked down to those who need access and are only available to those using an approved key. However, when you don’t set up the correct permissions for users, you can impede the application’s basic functionality. 

If you’re using an external API, like Facebook, Twitter, or even Google Analytics, make sure you’re adding the permissions for your users to access the data they need. Also, keep on top of any newly added features that can increase security risks. 

How to Fix Incorrect API Permissions

If you’re leveraging external APIs requiring extra configuration, get the correct API key so the app has the proper permissions. Also, provide your clients with API keys relevant to their authorization levels. Thus, your users will have the correct permissions and will seamlessly access your application.

2. Unsecured Endpoints and Data Access Tokens

We’ve all seen it happen a million times: someone discovers an API that’s exposed to everyone after gaining user consent. Until now, this was usually reasonably benign, but when credentials are leaked, things can get ugly fast, and companies lose brand trust. The biggest problem here is keeping admins from having unsecured access to sensitive data. 

How to Fix Unsecured Endpoints and Data Access Tokens

Using a secure key management system that includes the “View Keys” permission for the account will help mitigate this risk. For example, you could use AWS Key Management Service (AWS KMS) to help you manage and create your encryption keys. If you can’t protect your keys, then at the very least, include a strong master password that all users can access, and only give out these keys when needed. 

3. Invalid Session Management

Untrusted tokens and session variables can cause problems for how a website functions, causing timing issues with page loads and login calls or even creating a denial of service, which can harm the end-user experience and your brand. 

How to Fix Invalid Session Management

The best way to secure sensitive data is by using token authentication, which will encode user data into the token itself based on time/date stamps. You can then enforce this to ensure that whenever you reissue tokens, they expire after a set amount of time or use them for API requests only. 

As for session variables, these are usually created based on your authentication keys and should be handled the same way as your privileged keys—with some encryption. And keep the source of your keys out of the hands of anyone who can access them. 

4. Expiring APIs

If you’re using an API to power a website, you must upload new data in real time or save it to a cache for later use. When you set an expiry time for an API and fail to update, you make it unavailable. When a user or application tries to access it after the expiry, they get a 404 or 500 error. 

How to Fix Expiring APIs

You should use a middle ground option—a proxy API. This will allow you to cache your data before you make it available and only allow access to the correct bits of the APIs as needed. You should also schedule tasks that run daily to import updated data and bring it into your system. 

5. Bad URLs

This one isn’t necessarily a mistake, but it happens from time to time when developers aren’t careful about how they name things or if they’re using an improper URL structure for their API endpoints

When the URL structure is too complex or has invalid characters, you will get errors and failures. Look at some examples of bad URL structure: 


The above structure is bad because the “?” character filters a single parameter, not the type of request. The default request type is GET; thus, a better URL would look like this: 


How to Fix Bad URLs

Remove any unsafe characters in your URL, like angle brackets (<>). You use angle brackets as delimiters in your URL. Also, design the API to make it more friendly for users. For example, this URL “https://example.com/users/name”  tells users they’re querying the names of users, unlike this URL “https://example.com/usr/nm” 

It’s also good practice to use a space after the “?” in your API URL because otherwise, people can mistakenly think that the space is part of a query string. 

6. Overly Complex API Endpoints

This happens when trying to build multiple ways of accessing multiple applications. You do this by relying on generic endpoints instead of target audiences and specific applications. Creating a lot of different paths for the same data results in non-intuitive routes. 

How to Fix Overly Complex API Endpoints

There are several ways to go about this, but for most, you want to use a network proxy system that can handle the different data access methods and bring it all into one spot. This will help minimize potential issues with your APIs routes and help with user confusion and brand damage. 

7. Exposed APIs on IPs

This can happen when organizations are not properly securing their public IP addresses, or there is no solid monitoring process. This exposes your assets by providing easy access to anyone. Exposed IPs make your application vulnerable to DDOS attacks and other forms of abuse or phishing. 

How to Fix Exposed APIs on IPs

Make sure you properly manage your IP addresses and have a solid monitoring system. You must block all Ipv6 traffic and enforce strict firewall rules on your network. You should only allow service access through SSL, HSTS, or other TLS methods. 


API errors are a plague on the internet. Sometimes they come as very poor performance that can produce long response times and bring down APIs, or they can be network-related and cause unavailable services. They’re often caused by problems such as inconsistent resource access errors, neglect in proper authentication checks, faulty authentication data validation on endpoints, failure to read return codes from an endpoint, etc. Now that you know what causes API failures and how to fix them, you need to complement this with Traceable AI, a platform with products to help you analyze and protect your application from risk and thus prevent failures. 

About Traceable

Traceable is the industry’s leading API security platform that identifies APIs, evaluates API risk posture, stops API attacks, and provides deep analytics for threat hunting and forensic research. With visual depictions of API paths at the core of its technology, its platform applies the power of distributed tracing and machine learning models for API security across the entire software development lifecycle. Book a demo today.


This post was written by Mercy Kibet. Mercy is a full-stack developer with a knack for learning and writing about new and intriguing tech stacks.