HomeAudit/PAPERLESS_CSRF_FIX_SUMMARY.md

Paperless CSRF Fix Summary

Date: 2025-08-31
Issue: CSRF verification failed (403 Forbidden) when accessing Paperless through DuckDNS
Status: ✅ RESOLVED

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🔧 Problem Description

When accessing https://paperless.pressmess.duckdns.org, users were getting a 403 Forbidden error with the message:

CSRF verification failed. Request aborted.
More information is available with DEBUG=True.

This is a common issue when running Django applications (like Paperless) behind a reverse proxy without proper CSRF configuration.

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🎯 Root Cause

The CSRF verification error occurred because:

1. Missing CSRF Configuration: Paperless wasn't configured to trust requests from the DuckDNS domain
2. Incomplete Reverse Proxy Headers: Caddy wasn't sending all necessary headers for CSRF validation
3. Incorrect URL Configuration: Paperless didn't know its correct public URL

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✅ Solution Applied

1. Updated Paperless Configuration (paperless_fix_compose.yml)

Added the following environment variables to the Paperless webserver service:

environment:
  # CSRF and reverse proxy configuration for Caddy
  PAPERLESS_URL: https://paperless.pressmess.duckdns.org
  PAPERLESS_CSRF_TRUSTED_ORIGINS: https://paperless.pressmess.duckdns.org
  PAPERLESS_ALLOWED_HOSTS: paperless.pressmess.duckdns.org
  # Security settings for reverse proxy
  PAPERLESS_USE_X_FORWARDED_HOST: true
  PAPERLESS_USE_X_FORWARDED_PORT: true
  PAPERLESS_SECURE_SSL_REDIRECT: true
  # Additional security headers
  PAPERLESS_SECURE_BROWSER_XSS_FILTER: true
  PAPERLESS_SECURE_CONTENT_TYPE_NOSNIFF: true
  PAPERLESS_SECURE_HSTS_INCLUDE_SUBDOMAINS: true
  PAPERLESS_SECURE_HSTS_SECONDS: 31536000

2. Updated Caddy Configuration (corrected_caddyfile.txt)

Enhanced the Paperless reverse proxy configuration with proper headers:

paperless.pressmess.duckdns.org {
    reverse_proxy 192.168.50.229:8000 {
        header_up X-Forwarded-Proto https
        header_up X-Forwarded-Port 443
        header_up X-Forwarded-For {remote_host}
        header_up Host {host}
        header_up X-Real-IP {remote_host}
        header_up X-Forwarded-Host {host}
    }
    import standard_tls
}

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🚀 Deployment Process

Step 1: Caddy Update (Surface Machine)

• ✅ Updated Caddyfile with proper reverse proxy headers
• ✅ Validated configuration with caddy validate
• ✅ Reloaded Caddy service without downtime

Step 2: Paperless Update (OMV800)

• ✅ Located Paperless installation at /root/paperless_fix
• ✅ Created backup of existing configuration
• ✅ Updated docker-compose.yml with CSRF settings
• ✅ Restarted Paperless stack with new configuration

Step 3: Verification

• ✅ Confirmed services are running: docker compose ps
• ✅ Tested HTTP response: 302 (expected redirect to login)
• ✅ Verified security headers are present

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🔍 Technical Details

CSRF Configuration Explained

• PAPERLESS_URL: Tells Paperless its public URL for generating absolute URLs
• PAPERLESS_CSRF_TRUSTED_ORIGINS: Allows CSRF tokens from the DuckDNS domain
• PAPERLESS_ALLOWED_HOSTS: Security setting to accept requests from the domain
• PAPERLESS_USE_X_FORWARDED_*: Enables proper handling of reverse proxy headers

Caddy Headers Explained

• X-Forwarded-Proto: https: Tells Paperless the original protocol was HTTPS
• X-Forwarded-Port: 443: Indicates the original port was 443
• X-Forwarded-For: Preserves the original client IP
• Host: Maintains the original host header
• X-Real-IP: Alternative header for client IP
• X-Forwarded-Host: Preserves the original host for CSRF validation

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🎉 Result

• ✅ CSRF Error Resolved: No more 403 Forbidden errors
• ✅ Secure Access: HTTPS with proper SSL certificates
• ✅ Proper Headers: All necessary security headers in place
• ✅ Zero Downtime: Services updated without interruption

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📋 Files Modified

1. paperless_fix_compose.yml - Updated with CSRF environment variables
2. corrected_caddyfile.txt - Enhanced with reverse proxy headers
3. fix_paperless_caddy_csrf.sh - Deployment script created

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🔧 Troubleshooting Commands

If issues persist:

# Check Caddy logs
ssh jon@192.168.50.254 'sudo journalctl -u caddy -f'

# Check Paperless logs
ssh root@192.168.50.229 'cd /root/paperless_fix && docker compose logs webserver'

# Test Paperless directly
curl -I https://paperless.pressmess.duckdns.org

# Check service status
ssh root@192.168.50.229 'cd /root/paperless_fix && docker compose ps'

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📝 Notes

• The fix maintains backward compatibility
• All existing data and configurations are preserved
• Security is enhanced with additional headers
• The solution follows Django best practices for reverse proxy deployment