"HTTP error" Uploading Images to the Media Library

What’s actually happening

You drag an image into the Media Library, the progress bar crawls partway, then it dies with a red "HTTP error" and nothing else. The same file sometimes uploads on a retry, or a smaller image goes through fine. The message is generated client-side when the async request to async-upload.php fails or times out, so the real reason is in the server logs, not on screen.

Common causes

• PHP memory_limit too low for WordPress to generate the resized thumbnail set from a large image
• The image library (ImageMagick or GD) is missing, misconfigured, or chokes on the file's color profile/format
• The upload exceeds upload_max_filesize, post_max_size, or hits max_execution_time on a slow resize
• A security plugin or mod_security rule blocks the POST to async-upload.php (special characters in the filename trigger this often)
• A reverse proxy/CDN (Cloudflare) request size or timeout cap cuts the upload short

How to fix it

1. Read the actual error before guessingOpen the browser Network tab, retry the upload, and click the failed async-upload.php request. A 500 points at PHP/memory, a 403 points at a security rule/WAF, a 503 or timeout points at the resize taking too long. Cross-reference the PHP error log (cPanel -> Errors or /var/log).
2. Raise PHP memory and limitsSet WP_MEMORY_LIMIT to 256M in wp-config.php, and bump memory_limit, upload_max_filesize, post_max_size, and max_execution_time in php.ini or .user.ini. Thumbnail generation from a 5000px photo can need far more memory than the source file size suggests.
3. Rule out the image processorInstall the Health Check plugin or check Tools -> Site Health -> Info -> Media Handling. If ImageMagick is flagged as broken, switch WordPress to GD by adding a filter that returns 'WP_Image_Editor_GD' first, then retry. A corrupt CMYK or oddly-profiled JPEG will fail in Imagick but convert fine in GD.
4. Disable security plugins / mod_security to isolateTemporarily deactivate Wordfence/iThemes or have your host disable mod_security, then upload again. If it works, re-enable and whitelist async-upload.php instead of leaving protection off. Rename files with apostrophes, ampersands, or non-ASCII characters before upload.
5. Re-save the image and shrink itExport the file as a clean sRGB JPEG/PNG under ~2MB and re-upload. Oversized originals and exotic formats are the single most common trigger; resizing before upload sidesteps the resize that was failing.