Practical working guide
A safe attachment workflow for website enquiries
Handle enquiry attachments through a restricted upload and review workflow: accept only needed formats, limit size, validate files on the server and control who can retrieve them. Do not treat a filename or browser-supplied content type as proof that a file is safe.
Turn the requirements into a developer handoff
OWASP recommends layered file-upload protection, including extension, type, size and access checks. The checklist below is an operational handoff, not evidence that a particular form already enforces these controls.
| Decision | Fill in before launch |
|---|---|
| Business need | Which document is genuinely needed at this stage? |
| Allowed formats and size | Explicit allowlist and request limits |
| Storage and access | Non-public location, authorised retrieval and expiry |
| Validation and scanning | Server checks, quarantine and failure response |
| Retention owner | Who deletes files when the purpose ends? |
Sources: OWASP File Upload Cheat Sheet.
Worked test record
Fictional example: a survey form needs one floor-plan PDF, not identity documents. An authorised reviewer sees the submission only after validation; another customer cannot retrieve it. Test a harmless allowed file, an oversized file, a renamed disallowed file and an unauthorised download. Record expected result, actual result and evidence for each. A rejected upload should leave a clear message and preserve the rest of the enquiry where safe.
When a file cannot be accepted
Offer a secure alternative agreed with your technical team; do not ask customers to make private documents public. Keep suspicious content quarantined and follow your incident process. Recheck the workflow whenever allowed formats, storage or access rules change.