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File upload security policy builder

Describe your upload rules and get a policy document plus server-side enforcement snippets for Nginx, Express, or ASP.NET Core.

Describe the uploads, the allowlist, and a size cap to build the policy.

The principle behind every line: only server-side checks are security controls. The extension on a filename is a claim, the stored bytes are the evidence; that is why the snippets read the file header against a signature table instead of trusting the MIME header. Honest limits of this builder: it writes templates, not reviewed code; its signature table covers common families (PNG, JPEG, GIF, WebP, PDF, ZIP-based office files, MP4, and more) and names any extension it cannot check rather than inventing one; and it cannot scan files or re-encode them here. Those steps exist as hooks in the code for your server to run.

Your upload rules

What are you accepting?Up to 500 characters, becomes the policy's scope

Generate code forEvery snippet enforces on the server; nothing here trusts the browser

Allowed extensionsComma separated. An allow-list, never a block-list

Expected MIME typesClaims the stored bytes must confirm, comma separated

Maximum size (MB)Up to 2,048 MB, fractions fine

Rename on storageThe stored name is generated server-side; the client's name stays display metadata

Re-encode imagesDecoding and re-encoding strips EXIF GPS and beats validating bytes

Serve from a separate originA dedicated hostname that shares no cookies or script context with the app

Require authenticationThe check runs before the body is parsed or stored

Malware scanningScans must fail closed: an unavailable scanner rejects the upload

The builder always writes the safe storage pattern (server-generated names), whether or not the box is checked; the flag decides how the policy words the rule.

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File upload security policy builder

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