playbookSecurity Playbooks~1 min readUpdated Apr 23, 2026

Inspect File Upload Surface

Goal

Determine whether upload features create unsafe execution, storage, parser, or exposure paths.

Assumptions

uploads may be validated weakly
post-processing is often riskier than the upload itself
storage and serving paths may cross trust boundaries

Prerequisites

one or more upload or import features
ability to inspect storage, response behavior, or processing side effects where authorized

Recon steps

Map all upload and import entry points.
Identify where files are stored, transformed, previewed, or served.
Note allowed extensions, MIME handling, naming, and public exposure.

Exploit / test steps

Compare extension checks vs actual parser behavior.
Test whether uploaded content is served back from executable or overly trusted contexts.
Probe archive and document processing paths.
Inspect filename handling and path assumptions.
Look for predictable public URLs or indirect exposure of stored files.

Validation clues

unsafe file types accepted or mishandled
uploaded content becomes publicly reachable unexpectedly
processing path reveals parser or storage issues
files can influence downstream rendering or server behavior

Mitigation

validate more than extension alone
isolate storage and serving paths
avoid execution-capable contexts
review previews/transforms as part of the attack surface
use indirect references and safe naming

Logging / detection

unusual upload MIME/type combinations
repeated failed processing attempts
public access to files that should remain private

References

Testing / Lab: PortSwigger file upload vulnerabilities — https://portswigger.net/web-security/file-upload
Foundational: OWASP WSTG — https://owasp.org/www-project-web-security-testing-guide/latest/