How to Fix the 400 Bad Request Error in WordPress

How to Fix the 400 Bad Request Error in WordPress

Seeing a “400 Bad Request” error on your WordPress site? This browser-server communication issue means that the request sent by your browser was malformed or too large for the server to process.

The 400 error is often related to corrupted cookies, URL formatting issues, or server misconfigurations—and it can usually be fixed with a few simple steps using cPanel and browser tools.

What Causes a 400 Bad Request Error?

- Corrupted browser cookies or cache
- Improperly encoded URLs or special characters
- Overly long request headers or cookies
- File size limits exceeded (during uploads)
- Security plugin blocks or ModSecurity rules

Step-by-Step Guide to Fix the 400 Bad Request Error

1. Clear Browser Cookies and Cache

Corrupted cookies or session data are the most common cause.

- Clear all cookies and cache for your domain
- Restart your browser and try accessing the site again
- Alternatively, use an incognito/private window

2. Check URL for Typos or Special Characters

If the error appears only on specific pages:

- Double-check the URL for spaces, symbols, or malformed query strings
- Use URL encoding tools for links containing special characters

3. Rename or Delete Corrupted .htaccess File

A broken or conflicting .htaccess file can trigger 400 errors.

- In cPanel > File Manager > public_html
- Rename your .htaccess file to .htaccess_old
- Reload your site

If it works, regenerate the file in WordPress: Dashboard > Settings > Permalinks > Save Changes

4. Disable Security Plugins Temporarily

Security plugins might block legitimate requests.

- Go to wp-content/plugins in File Manager
- Rename folders of security plugins (e.g., wordfence → wordfence_old)
- Refresh the site to see if the error is resolved

5. Check ModSecurity Logs

ModSecurity may block requests that exceed certain header or cookie sizes.

- In cPanel > Security > ModSecurity
- Disable ModSecurity temporarily for your domain and test again
- If successful, re-enable and contact support to whitelist your request

6. Increase Upload Limits (If Error Occurs During File Uploads)

The server may reject large files during upload.

- Go to cPanel > MultiPHP INI Editor
- Adjust:
 - upload_max_filesize = 64M
 - post_max_size = 64M
 - max_input_vars = 3000

7. Inspect Server Logs

To dig deeper:

- In cPanel > Metrics > Errors
- Look for entries with “400” status codes and clues on the exact issue

Final Thoughts

The 400 Bad Request error in WordPress is often caused by browser-side corruption or simple misconfigurations. By clearing cookies, fixing .htaccess, and adjusting server limits, you can resolve it in minutes.

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At RDPCore.com, we help you avoid 400 errors with:

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