Evidence review
What to inspect before changing anything
Start with the delivered website and the real user journey. Record the current state so the team can distinguish an observed problem from an assumption and compare the same surface after deployment.
- 01List accepted formats, sizes and audiences
- 02Inspect content signatures rather than extensions alone
- 03Review storage location and download headers
Implementation
A practical improvement plan
Make the smallest coherent change that solves the observed problem. Keep normal code review, accessibility, security and product checks in the loop instead of optimizing for the scan alone.
- 01Generate server-side names and isolate storage
- 02Re-encode supported media when practical
- 03Scan risky formats and restrict public delivery
Verification
How to verify the result
Verification should test the intended outcome and the most likely regression. Use the production delivery path whenever headers, caching, rendering or third-party services affect the result.
- 01Upload mismatched, oversized and polyglot files
- 02Test direct object access and caching
- 03Confirm content is served with safe types and disposition
Common pitfall
A shortcut to avoid
An extension allowlist alone does not establish what bytes were uploaded or how browsers will interpret them.
Further reading
Primary guidance and references
These sources provide standards, security guidance or the interpretation framework used to keep this guide bounded. Product-specific implementation still requires review in the actual codebase.