System Security / 2026 Essentials
Document Uploads Need More Than a File Extension Check
Protect upload, storage, and processing stages before accepting business documents.
Environment and inputs: A disposable upload service, harmless allowed and disallowed file fixtures, size limits and separate test download identities.
An uploaded file can attack a parser, consume storage, or expose information through public retrieval. OWASP recommends layered controls because no single file check is sufficient. This matters especially when documents are passed onward to OCR, search indexing, or an AI assistant.
What matters
- Allow only required file types and validate more than the user-supplied content type.
- Generate safe storage names, limit file sizes, and store uploads outside executable web paths.
- Restrict access and use appropriate scanning or isolation before further processing.
Practical example: A support portal stores attachments privately and permits staff to retrieve them only through an authorised download handler.
One action today: Check whether an uploaded attachment can be accessed without permission or executed as code.