duo.file.force.com is a subdomain under Salesforce's force.com platform. When you visit it, you're immediately redirected to duo.my.salesforce.com, which is a classic pattern for a Salesforce customer portal or internal app. This is likely used by Duo Security (now part of Cisco) for file sharing or support access.
From a security standpoint, the site checks all the boxes: valid SSL, enforced HTTPS, and protection against clickjacking and other browser attacks. It's clean on all blacklists we checked. The technical infrastructure is exactly what you'd expect from a Salesforce-hosted service.
The biggest unknown is ownership. Subdomains under force.com don't have their own WHOIS records, so we can't confirm exactly who manages this particular one. The site also has no visible history in the Wayback Machine, meaning it's either brand new or not publicly archived. For a tool that may handle sensitive data, you'd ideally want clearer information about who's behind it — but the Salesforce association does provide a strong layer of trust.
If you're wondering whether duo.file.force.com is a scam, the evidence doesn't support that. It's more likely a legitimate, if opaque, business tool. Use standard precautions: make sure you're on the official Salesforce login page before entering credentials, and check that the URL matches what your organization provided. There are no obvious red flags here, just a lack of full transparency that's common for subdomains of larger platforms.