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/ogrodev/fsociety/payment-securitynpx skills add ogrodev/fsociety --skill payment-securitygit clone --depth 1 https://github.com/ogrodev/fsocietyWhat 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 | $0.00308 | $0.03284 |
| Opus 5 | $0.00154 | $0.01642 |
| Sonnet 5 | $0.00062 | $0.00657 |
| Haiku 4.5 | $0.00031 | $0.00328 |
Grade A, and why
payment-security scanned grade A with 0 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 2d 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.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 289 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Payment Security Testing
Payment systems are the highest-impact attack surface in any e-commerce application. A single vulnerability translates directly to financial loss, regulatory exposure, and reputational damage. Payment findings are almost always HIGH or CRITICAL severity -- a confirmed price manipulation or payment bypass is an automatic CRITICAL.
This skill covers the full offensive lifecycle against payment systems: flow mapping, price manipulation, race conditions, IDOR exploitation, gateway bypass, cart tampering, and refund abuse.
Triage Workflow
Follow this sequence. Each phase builds on the previous one. Skip nothing -- payment logic bugs hide in edge cases.
Phase 1 -- Payment Flow Mapping
Before attacking, map the entire payment lifecycle. Every request from cart to confirmation is in scope.
Map these flows:
- Add to cart -- item selection, quantity, variant, pricing source
- Cart management -- update quantity, remove items, apply coupons/discounts
- Checkout initiation -- address entry, shipping method selection, tax calculation
- Payment method selection -- card entry, saved card, wallet, gateway redirect
- Payment processing -- tokenization, charge creation, 3DS challenge
- Payment confirmation -- callback/webhook, order status update, fulfillment trigger
- Post-payment -- refund flow, cancellation, subscription management
Capture with HTTP Repeater:
Load: ToolSearch -> select:mcp__hexstrike-ai__http_repeater
Intercept the full checkout flow from cart to confirmation.
For each request, note:
- Which parameters control price, quantity, item identity
- Which parameters reference user identity (user_id, session, account)
- Where the server trusts client-supplied values vs. server-side lookup
- Where the flow can be short-circuited (skip steps, replay confirmations)
Key questions to answer during mapping:
- Does the server recalculate totals, or trust the client-submitted amount?
- Are item prices embedded in the request, or looked up by product ID?
- Is the payment amount derived from the cart at checkout time, or passed as a parameter?
- Does the webhook/callback validate the payment amount matches the order total?
- Can checkout steps be reordered or skipped?
What ships with it
6 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
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.
- 2d ago First seen · 289 lines · 308 tokens per session scan A 94e520ebda43
payment-security is a skill published in the GitHub repository ogrodev/fsociety (20 stars, last pushed 5mo ago), licensed MIT. It adds 308 tokens to every session and 3,284 once invoked, about $0.0015 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
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