Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx agentmods add skills/yaklang/hack-skills/http-parameter-pollutionnpx skills add yaklang/hack-skills --skill http-parameter-pollutiongit clone --depth 1 https://github.com/yaklang/hack-skillsWhat it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5 | $0.00062 | $0.01780 |
| Opus 5 | $0.00031 | $0.00890 |
| Sonnet 5 | $0.00012 | $0.00356 |
| Haiku 4.5 | $0.00006 | $0.00178 |
Grade C, and why
http-parameter-pollution scanned grade C with 1 finding against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 3d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Cloud metadata endpointhighServer-side request forgery
One request to 169.254.169.254 can return temporary IAM credentials.
url=https://allowed.cdn.example/&url=http://169.254.169.254/ Copies of this mod
2 near-identical copies found in the catalogue:
- http-parameter-pollution — 100% identical, 0 lines differ
- http-parameter-pollution — 94% identical, 4 lines differ
How it starts
The opening of the file, as written. The whole thing — 209 lines — stays where its author put it; the contents beside it link to each section on GitHub.
SKILL: HTTP Parameter Pollution (HPP)
AI LOAD INSTRUCTION: Model the full request path: browser → CDN/WAF → reverse proxy → app framework → business code. Duplicate keys (
a=1&a=2) are not an error at HTTP level; each hop may pick first, last, join, or array-ify. Test HPP when WAF and app disagree, or when internal HTTP clients rebuild query strings. Routing note: when the same parameter appears multiple times, or WAF/backend stacks differ, use the Section 1 matrix to test first/last/merge assumptions, then design Section 3 scenario chains.
0. QUICK START
Hypothesis: the security check reads one occurrence of a parameter while the action reads another.
First-pass payloads
id=1&id=2
id=1&id=1%20OR%201=1
url=https://legit.example&id=https://evil.example
amount=1&amount=9999
csrf=TOKEN_A&csrf=TOKEN_B
user=alice&user=admin
Body variants (repeat for POST)
application/x-www-form-urlencoded
id=1&id=2
multipart/form-data
------boundary
Content-Disposition: form-data; name="id"
1
------boundary
Content-Disposition: form-data; name="id"
2
Quick methodology
- Fingerprint front stack (CDN/WAF) vs origin (language/framework) using baseline
a=1&a=2. - Send both orders:
a=1&a=2anda=2&a=1(some parsers are order-sensitive). - If JSON: test duplicate keys and Content-Type confusion (see Section 2).
1. SERVER BEHAVIOR MATRIX
Typical defaults — always confirm; middleware and custom parsers override these.
| Technology | Behavior | Example: a=1&a=2 |
|---|---|---|
PHP / Apache ($_GET) |
Last occurrence | a=2 |
| ASP.NET / IIS | Often comma-joined (all) | a=1,2 |
| JSP / Tomcat (servlet param) | First occurrence | a=1 |
Python / Django (QueryDict) |
Last occurrence | a=2 |
Python / Flask (request.args) |
First occurrence | a=1 |
Node.js / Express (req.query) |
Array of values | a=['1','2'] (shape may vary by parser version) |
| Perl / CGI | First occurrence | a=1 |
| Ruby / Rack (Rack::Utils) | Last occurrence | a=2 |
Go net/http (ParseQuery) |
First occurrence | a=1 |
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 3d ago First seen · 209 lines · 62 tokens per session scan C d456fea84782
http-parameter-pollution is a skill published in the GitHub repository yaklang/hack-skills (2,004 stars, last pushed 2mo ago), licensed MIT. It adds 62 tokens to every session and 1,780 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it C with 1 finding (cloud metadata endpoint). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
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