Incident Report — Command Injection via Upload Form Field (Production Capture)

Original source: incident-report-upload-field-rce.md in the repository.

Companion to Mozi: RCE attempt. Real capture from a production Sentry deployment; attacker IPs are partially masked.

TL;DR

A scanner POSTed a multipart form with a command-injection payload hidden inside a form field's content — invisible to any filter that only inspects URLs, headers, or query strings. Sentry's request-body inspection parsed the multipart payload, scanned the field value, and emitted the rce signal from the body: 80/100 critical, blocked with 403. The attack surface here is exactly the one most WAF deployments miss.

Event summary

The signal chain

rce                — "upload field 0: cmd" — weight 70
method_not_allowed — "POST /"              — weight 10
──────────────────────────────────────────────────
score 80 → critical → verdict block → 403

The rce signal did not come from the URL (/ is empty of payloads) or from any header. It came from the body pipeline:

1. The edge buffered the request body within its inspection cap.
2. The multipart parser split the form into fields.
3. The upload_content heuristic scanned each field's text content and matched the cmd (command injection) text family in field 0.

The exact payload text is not persisted — Sentry records detection metadata, never raw bodies — but the match family is the same command-injection class as the Mozi captures: chained shell commands attempting execution on the server.

Why this demonstrates effectiveness

• Body-level inspection is table stakes for real RCE defense. Filter only the query string and this request scores a 10 and passes as a boring POST /.
• Detection survives transport. Whether injection arrives in a query string (Mozi: RCE attempt) or wrapped in multipart encoding, the same heuristic family fires after decoding — no bypass by re-encapsulation.
• Privacy held under attack conditions. Even while blocking a critical request, the pipeline persisted zero raw body bytes — detection metadata only.