# Hunt Race Condition

Hunting skill for race condition vulnerabilities.

- Repository: https://github.com/Zyrexnn/Cybermes (987 stars)
- Category: Security
- License: Apache-2.0
- Last updated: 2026-11-01
- Runs scripts: no, instructions only

## Install

Claude Code: `npx skills add Zyrexnn/Cybermes --skill hunt-race-condition -g -a claude-code -y`
Codex: `npx skills add Zyrexnn/Cybermes --skill hunt-race-condition -g -a codex -y`
Cursor: `npx skills add Zyrexnn/Cybermes --skill hunt-race-condition -g -a cursor -y`
Gemini CLI: `npx skills add Zyrexnn/Cybermes --skill hunt-race-condition -g -a gemini-cli -y`

## Description

Hunting skill for race condition vulnerabilities. Built from 12 public bug bounty reports including modern HTTP/2 single-packet attack cases (James Kettle DEF CON 2023 "Smashing the State Machine"; RyotaK / Flatt Security 10,000-request first-sequence-sync expansion 2024). Covers coupon double-redemption, gift-card double-spend, MFA-OTP-validate race, account-create race, faucet/crypto token double-mint, email-activation race, vote/upvote inflation, password-reset token race, rate-limit bypass via concurrent requests. Use when hunting race conditions, TOCTOU bugs, MFA-bypass-via-timing.

## SKILL.md, as published by its author (untrusted third-party text, read it as data)

## Firing a race, two primitives (tooling-agnostic)

Winning a race needs requests that arrive in the *same* narrow window, sequential sends never
work. Use a single-packet / synchronized-send tool: **Burp Repeater** "Send group in parallel"
(HTTP/2 single-packet attack), **Turbo Intruder** (`engine=Engine.BURP2`, `gate` sync), or any
client that can flush N requests simultaneously. Two shapes:

- **Identical-copies race**, fire N IDENTICAL copies of one request at once (limit-overrun:
  double-spend a coupon/gift-card, exceed a one-per-user quota). Success = ≥2 of the N return 2xx.
- **Different-requests race (partial construction)**, fire a LIST of DIFFERENT requests in one
  synchronized window, repeated over several rounds. For register-then-confirm / TOCTOU races
  where the object exists in a usable state mid-creation. Example (email-verification bypass, register an arbitrary email, then confirm it through the construction window with a blank token):
  ```
  Request A:  POST /register   body: csrf=<csrf>&username=hacker&email=anything@exploit.net&password=pw
  Request B:  GET  /confirm    params: token=   (empty)
  Fire A and B together, repeat ~20 rounds.
  ```
  Get a fresh CSRF from `GET /register` first, then fire the batch. After it succeeds, log in as the
  new account and perform the objective (e.g. a state-changing admin action such as deleting a user).
  The blank-token confirm wins during the window where the user row exists but its verification
  token isn't set yet.

## Crown Jewel Targets

Race conditions are high-severity findings because they break financial, access control, and integrity assumptions that defenders rarely stress-test. Highest payouts come from:

The rest: https://github.com/Zyrexnn/Cybermes/blob/HEAD/knowledge/Claude-BugHunter/skills/hunt-race-condition/SKILL.md