CVE-2021-3313: Plone XSS in User Fullname Property and File Upload

The vulnerability manifests in two key areas: 1) User profile handling - the fullname field update mechanism lacks proper output encoding when rendering user-controlled data in templates like ownership views. 2) File upload processing - SVG/HTML files with embedded scripts are stored and served with executable MIME types (image/svg+xml) without Content-Disposition headers or sanitization. The combination of improper input handling in user properties and insufficient file content validation creates XSS vectors. These conclusions align with the attack examples in Compass Security's advisory and the hotfix descriptions that specifically mention these components.