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HUNT-EXCEPTIONAL-CONDITIONS — Verbose Errors / Fail-Open (A10:2025)
What actually pays
Well-built apps catch errors and return a clean, generic message. A broken app, when handed input it didn't expect, throws an unhandled exception and renders a developer error page straight to the client — leaking the stack trace, the ORM/query internals, server-side file paths, and framework/library versions. That disclosure is the finding (and it arms SQLi/RCE/path attacks next).
Recon
Any endpoint that parses input is a candidate; the richest are:
JSON APIs that expect typed fields: POST /api/* with {numbers, ids, enums}
Endpoints with numeric/id path or query params: /item/{id}, ?page=, ?quantity=
Search / filter / sort params
File or content-type sensitive uploadsAttack — send what the code didn't anticipate
Take a known-good request and break ONE assumption at a time:
- Wrong type: a field the app expects to be a number/string is sent as an
array or object — {"rating":"x","comment":[1,2,3]}, {"quantity":{}}.
- Malformed body: truncated/!invalid JSON, an unterminated string, a stray
brace, a wrong/missing Content-Type.
- Boundary/oversized: a very long string, a huge/negative/overflow number.
- Null byte / control chars embedded in a value.
POST /api/Feedbacks {"rating":"notanumber","comment":[1,2,3]}
GET /item/' OR /item/%00 (also exercises the error path)Watch the RESPONSE BODY, not just the status: a 500 (or even a 200/400) whose body contains a stack trace or framework error page is the signal.
What counts as a leak (the success signal)
A finding is confirmed when the response body contains a cross-framework error-disclosure signature:
- Node/Express + Sequelize:
SequelizeDatabaseError,node_modules/sequelize,
a JS stack with internal paths.
- PHP:
<b>Warning</b> ... /var/www/.../file.php on line N. - Python:
Traceback (most recent call last),werkzeug.exceptions. - Java:
at com.app.Foo(Foo.java:42)stack frames. - .NET:
Server Error in '/' Application, a[System.XxxException: ...]YSOD.
A clean JSON error ({"error":"Invalid input"}) with no internals is NOT a finding — that's correct handling. Disclosure of internal structure is.
Validation discipline
- Capture the exact leaked artifact (path, ORM class, version, stack frame) —
that's the evidence. "It returned 500" alone is not disclosure.
- Note what the leak enables next (e.g. a disclosed SQL error → hunt-sqli; a
disclosed absolute path → hunt-lfi).
