Symptoms

Your site is hosted on an Apache server, and you are downloading the Prime Mover package using Firefox. For some reason, you paused the download, and when you resume it, it can no longer be resumed. The only way to fix it is to repeat the download process from scratch.

Affected environment

This issue is only reproducible if all of the conditions below are true:

  • Apache server.
  • PHP-fpm.
  • Firefox

Cause of issue

The Root Cause (CVE-2024-24795)

  • The Vulnerability: Apache introduced a security patch to fix CVE-2024-24795. This vulnerability allowed malicious actors to perform HTTP Response Smuggling and Response Splitting attacks by manipulating headers sent from backend scripts.
  • Apache’s Solution: To block this attack vector, newer Apache updates automatically strip or ignore the Content-Length header generated by backend scripts running through FastCGI/PHP-FPM.
  • The Side Effect: While this protects the server, it breaks custom PHP download classes. Because Apache drops the Content-Length header your script calculates, Firefox (which strictly enforces HTTP specifications) sees a corrupted payload structure during pause/resume requests and refuses to resume the download.

Does it affect other browsers?

No, only Firefox.

Why Chrome works: When Chrome pauses and resumes a download, if it receives a 200 OK or missing length metadata, it is highly permissive and tries to guess the boundaries or read the stream anyway.

Why Firefox fails: Firefox is incredibly strict about HTTP specifications. When you try to resume, Firefox expects a rock-solid matching Content-Length and a proper 206 Partial Content response metadata bundle. Because Apache strips the Content-Length passed by your PHP class, Firefox sees a corrupted or missing payload structure, panics, and refuses to resume.

The Fix

Add this to the top of your WordPress .htaccess:

# --- START RESUMABLE DOWNLOAD FIX FOR FIREFOX ---
<IfModule mod_env.c>
    # Try setting the standard variable
    SetEnv ap_trust_cgilike_cl 1
    # Try setting the prefixed version to guarantee PHP-FPM reads it correctly
    SetEnv REDIRECT_ap_trust_cgilike_cl 1
</IfModule>

<IfModule mod_rewrite.c>
    <IfModule !mod_env.c>
        RewriteEngine On
        # Fallback using mod_rewrite flags if mod_env is disabled
        RewriteRule .* - [E=ap_trust_cgilike_cl:1,E=REDIRECT_ap_trust_cgilike_cl:1]
    </IfModule>
</IfModule>
# --- END RESUMABLE DOWNLOAD FIX FOR FIREFOX ---

Once the .htaccess is updated, clear your browser cache and re-test. When you resume it, it will work.

Still cannot download?

You can always download the WPRIME package created by Prime Mover in several ways. Feel free to check this tutorial on alternative methods to download the package.

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