prototype-pollution

prototype-pollution is a skill for Claude Code, Codex from jinyimeng01/mastermind-bug-bounty. It costs 72 tokens per session (1,898 once invoked), scanned A, original, no licence file.

A guide to finding prototype pollution, a JavaScript or Python flaw where attacker-controlled data changes shared object or class behavior. It also covers chains that may lead to code execution or cross-site scripting (XSS).

In plain words
What is it for?
Use it to review merge functions, deep-copy utilities, browser object handling, DOMPurify, jQuery, and template engines such as EJS, Pug, and Handlebars.
Why use it?
It helps trace a seemingly small data-handling bug to a serious result, such as running server code or injecting browser scripts.

Skill for Claude CodeCodex

Install

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.

agentmods
npx agentmods add skills/jinyimeng01/mastermind-bug-bounty/prototype_pollution
Any agent
npx skills add jinyimeng01/mastermind-bug-bounty --skill prototype_pollution
Clone the repo
git clone --depth 1 https://github.com/jinyimeng01/mastermind-bug-bounty

Made for: Claude Code, Codex.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for prototype-pollution

README.md
[![agentmods](https://agentmods.dev/badge/skills/jinyimeng01/mastermind-bug-bounty/prototype_pollution.svg)](https://agentmods.dev/skills/jinyimeng01/mastermind-bug-bounty/prototype_pollution)
Your own site
<a href="https://agentmods.dev/skills/jinyimeng01/mastermind-bug-bounty/prototype_pollution"><img src="https://agentmods.dev/badge/skills/jinyimeng01/mastermind-bug-bounty/prototype_pollution.svg" alt="Measured on agentmods" height="20"></a>
Per session 72 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,898 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 2 findings. Scan, not verified.
Origin unknown No closer match found in the catalogue.
Token cost

What 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.

ModelPer sessionOnce invoked
Fable 5 $0.00072 $0.01898
Opus 5 $0.00036 $0.00949
Sonnet 5 $0.00014 $0.00380
Haiku 4.5 $0.00007 $0.00190

Measured 5d ago against content hash b519ae73d164, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

prototype-pollution scanned grade A with 2 findings 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 5d 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.

Makes network callslowCapability

Not a fault in itself. Listed so you know the mod talks to something, and to what.

resp = fetch(f"{{target}}{endpoint}",

Runs shell commandslowCapability

Expected in a hook, worth knowing in a rule or an instructions file.

"outputFunctionName": "x;process.mainModule.require('child_process').execSync('id');s"
skills/prototype_pollution/SKILL.md · 297 lines

The source is not reproduced here

No licence file

A repository with no LICENSE is all rights reserved by default, so the body is not copied here. The metadata, the measurements and the link are.

Read it on GitHub

Changes

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.

  1. 5d ago First seen · 297 lines · 72 tokens per session scan A b519ae73d164

Subscribe to this mod's changes

prototype-pollution is a skill published in the GitHub repository jinyimeng01/mastermind-bug-bounty (56 stars, last pushed 2mo ago), with no licence file. It adds 72 tokens to every session and 1,898 once invoked, about $0.0004 per session on Opus 5. A static security scan graded it A with 2 findings (makes network calls, runs shell commands). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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