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Home / windows-fixes / How to Fix Cloudflare 521 Error with Firewall Settings - Fix Windows Defender Real-Time Protection After Clean Boot-Fix 'pip install' Permission Denied on Ubuntu

How to Fix Cloudflare 521 Error with Firewall Settings - Fix Windows Defender Real-Time Protection After Clean Boot-Fix 'pip install' Permission Denied on Ubuntu

Updated 2026-07-29 02:49:29windows-fixes
How to Fix Cloudflare 521 Error with Firewall Settings - Fix Windows Defender Real-Time Protection After Clean Boot-Fix 'pip install' Permission Denied on Ubuntu
Likely symptom
Likely cause
Safe rollback

Verification route

  • Repeat the original action, not only a simplified test case.
  • Restart the app or reload the service after configuration changes.

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