How to Fix: Your client has issued a malformed or illegal request

The inability to access a website could be due to various reasons. While errors could be attributed to the server-side, a few could be related to the problems arising from the client, aka user. And Error 400 belongs to the latter half.

The accompanying error message reads Bad Request – Your client has issued a malformed or illegal request, which concretes our above statement. As a result, while the request leaves your PC, it wouldn’t be able to be carried forward by the servers.

So what could be the reason for this issue? An incorrect URL or a browser using an outdated browser cache or stored DNS records are the two most common causes of the error, as mentioned above.

Related: How to Fix: Chrome Not Loading Page (Display Only Text)?

While the issue is undoubtedly quite concerning and irritating in equal measures, fortunately, some workarounds are known to rectify this issue. And this guide shall make you aware of just that.

Recheck URL Format

One of the primary reasons for this issue is the entering of incorrect URLs by the user. In this regard, you should double-check the spelling of the website if you have mistakenly used backslashes instead of forward slashes or have incorporated an unsupported symbol, such as curly brackets, in the hyperlink.

Furthermore, although the site’s name isn’t case-sensitive, its directory might be. Just verify that everything is entered after the .com domain is precisely as it should be. Keep these points in mind and see if you can access the site.

Try Incognito Mode

It is no secret that third-party add-ons could lead to various 4XX errors. Therefore the safest bet is to browse the web in private mode in Chrome. Doing so will disable all the extensions, and if it fixes the issue as well, then the next course of action is to disable or remove the newly installed add-ons.

Here are the steps to open the incognito mode in Chrome:

1. Launch the Google Chrome browser.
2. Keypress the Ctrl + Shift + N shortcut keys to open an Incognito Window.
   
3. Now try accessing the site that was causing the bad request error.

If it loads without any issue, the problem could presumably be attributed to the installed extensions or cookie and cache clutter within the browser.

Disable Browser Extension

Most of the issue while accessing the browser is generally caused due to extensions that we have installed. Even I faced the issue with the website not loading correctly and found the extensions were the culprit. I think these browser extensions could result in malformed or illegal requests.

Here are the quick steps to disable browser extensions in Chrome:

1. Launch the Google Chrome browser on the computer.
2. Visit the chrome extensions pages at chrome://extensions/ address.
3. Toggle the button to disable the extension.
   
4. Now disable each extension, one at a time, until the error has been fixed.

Moreover, it is recommended to uninstall the extensions causing extensions immediately.

While these add-ons add more functionalities to the browser, they could sometimes lead to a few problems. As and when that happens, it is better to bid farewell to that extension.

Delete DNS Cache

DNS is a record book that holds all the Domain Names corresponding to their IP Addresses. But if this data gets outdated or corrupted, the browser wouldn’t establish a successful connection to the web. Therefore, it is recommended to delete the temporary cached data.

Here are the steps to clear the DNS cache from the Windows OS:

1. Open the Start Menu and search CMD.
2. Launch the Command Prompt as an administrator.
   
3. Now type in ipconfig /flushdns, and hit Enter.
   

This will delete the DNS cache, and hopefully, the lousy request will rectify the issue.

Flushing the DNS might delay the website’s loading the next time you visit them. However, this is a one-time delay and will be rectified as soon as the cache data is re-populated.

Delete Browser Cache and Cookies

Over time, a lot of temporary data in the browser gets accumulated. This not only slows down the browsing experience but could also conflict with the proper loading of websites. So should consider deleting these cache and cookies files at the earliest.

Here are the steps to clear browser cache and cookies:

1. Launch the Chrome browser.
2. Type in delete cache  chrome actions in the address bar.
3. Click on Clear Browsing Data from the drop-down menu.
   
4. Select Cookies and other site data and Cached images and files.
   
5. Hit the Clear data button and wait for the process to complete.

Check if it fixes the 400 Bad Request Error within the browser.

Deleting the cookies might erase some of the saved information. Likewise, deleting the cache would translate to the browser asking for a few extra seconds before loading a site. But both of them should be fine if they fix the underlying issue.

Verify File Size

If you are getting this error while trying to upload a file, it could be due to the maximum file size restriction placed by that site. So consider compressing this file to a RAR or ZIP format before uploading it to the web. Or, if possible, upload the file to the cloud and share the link with the concerned party.

Bottom Line: Fix 400 Bad Request

So this was all from this guide on how to fix the 400: Bad Request – Your client has issued a malformed or illegal request error. We have shared five different methods for the same.

In my case, the DNS cache wasn’t in sync with the online records. As a result, the browser was still picking up old pieces of data and, in turn, couldn’t establish a successful connection. Deleting this Domain Name Server cache proved to be the savior in my case.

Related: How to Fix: Is your connection private on Chrome?

Please let us know in the comments which spelled out success for you. Also, share if you have tried anything that worked to fix the issue.