Individual skill
web-http-parameter-pollution
Send the same parameter more than once so the WAF/validator and the backend disagree on which value wins — bypassing filters, access control, or business logic. Load on "HPP", when a value is validated at one layer but used at another, or when a WAF blocks a payload you need to slip past. Signals: proxies/gateways in front of the app, duplicated params reflected inconsistently.
skills/web/web-http-parameter-pollution/SKILL.md
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# HTTP parameter pollution
## When it applies
A request passes through more than one component that parses parameters — a WAF/gateway, then the
app; or a frontend that builds a backend request. If they resolve a duplicated parameter
differently, you can show one value to the guard and another to the logic.
## Why it works
There is no single rule for `?x=a&x=b`: PHP/Apache take the **last**, ASP/IIS **concatenates**
(`a,b`), classic JSP takes the **first**, Node/Express makes an **array**. When the validator and
the consumer sit on different stacks, a value that passes validation isn't the value that's used.
## Method
1. **Map the parsing**: send `?p=1&p=2` (and body dups) and observe which value the response reflects