File Upload Security

This guide treats file upload, import, attachment, and media-processing workflows as a control boundary rather than a list of attack commands. First document who owns it, who should reach it, what identity context applies, and which data or downstream systems it can affect.

• Confirmed asset owner and in-scope address or application.
• Expected clients, identities, and network zones.
• Protocol versions, encryption expectations, and authentication mode.
• Sensitive data classes and downstream dependencies.
• Monitoring owner, escalation contact, and agreed stop threshold.

1. 01

   Map allowed file types, size limits, owners, storage locations, processors, and delivery paths.

2. 02

   Create benign test files with unique identifiers.

3. 03

   Document authentication, authorization, scanning, retention, and deletion behavior.

4. 04

   Identify archive extraction and document-conversion components.

A useful result demonstrates a broken security expectation with a reversible, low-impact test. Scanner labels and version matches are leads; validate the actual control and preserve the clean baseline beside the changed request.

1. 01

   Verify allowlisted type and size enforcement using benign mismatches.

2. 02

   Confirm stored objects receive server-generated names and isolated permissions.

3. 03

   Test tenant and object authorization using synthetic files.

4. 04

   Check that processors fail safely and original uploads are not executed as active content.

ASSET / ENDPOINT:
SCOPE REFERENCE:
IDENTITY / NETWORK ZONE:
BASELINE:
CONTROL TESTED:
EXPECTED RESULT:
OBSERVED RESULT:
TIMESTAMP / REQUEST ID:
SANITIZED EVIDENCE:
STOP / CLEANUP STATUS:

• Log upload owner, object ID, type decision, scanner verdict, and processor outcome.
• Alert on repeated rejection, archive expansion, and executable content.
• Avoid logging file contents or sensitive filenames unnecessarily.

Keep raw data only when it is necessary to reproduce the finding. Redact credentials, session values, customer content, internal addresses, and personal data before evidence enters a ticket or report.

• Allowlist business-required types and verify content server-side.
• Store outside executable web roots with generated names.
• Scan and process in isolated environments.
• Enforce authorization again on download and deletion.