Hunting Race Conditions

A hunting playbook for race-condition / TOCTOU vulnerabilities, built from 12 public bug-bounty and coordinated-disclosure cases. Race conditions are high-severity because they break the financial, access-control, and integrity assumptions defenders rarely stress-test: double-spending credits, inflating votes, bypassing per-user limits, and racing token/state transitions. The enabling primitive for modern targets is the HTTP/2 single-packet attack, which collapses the race window to sub-millisecond and makes rate-limited, distributed, load-balanced backends race-able.

Quick-start

1. Enumerate one-time / limited-use actions — every endpoint enforcing "once per user", "limited quantity", or "deduct balance". The gap between its state read and state write is your window.
2. Capture a clean baseline request and confirm the expected single-use behaviour.
3. Stage parallel requests — prefer Turbo Intruder Engine.BURP2 (single-packet HTTP/2) when the target advertises h2; otherwise fall back to parallel HTTP/1.1.
4. Fire 10–50 simultaneous requests with last-byte sync, then look for multiple successes, duplicate effects, or stale-state where only one should have won.
5. Verify the effect and reproducibility (3/5 attempts), then run Gate 0 before reporting.

Full detail is loaded on demand — see References.

References

Each file is loaded on demand — read one only when the task needs that depth (progressive disclosure).

• references/methodology.md — crown-jewel targets, attack-surface signals (URLs, headers, JS/tech-stack tells), the 10-step hunting methodology, common root causes, defender bypass techniques, Gate 0 validation, and real impact examples · read when scoping targets, planning the hunt, or validating/writing up a finding.
• references/payloads.md — copy-paste Turbo Intruder, curl-parallel, and Python asyncio race templates, plus source-audit grep patterns and the HTTP/2 capability check · read when you need a ready-to-fire PoC or to audit source for unlocked read-then-write.
• references/single-packet-attack.md — the HTTP/2 single-packet deep reference: why it works, last-byte-sync mechanics, Wireshark validation, h2.0 vs h2.cl variants, race-window estimation, connection/stream shapes, the annotated Engine.BURP2 template, Flatt's first-sequence-sync (N>30), operator playbook, and anti-patterns · read when building or debugging a single-packet exploit or deciding which attack shape to use.
• references/disclosed-reports.md — the per-bug-class catalog of the 12 disclosed cases (GitLab CVE-2022-4037, Worldcoin, Stripe ×2, Reverb gift card, Cosmos faucet, InnoGames, Flatt PIN-bruteforce, nopCommerce CVE-2024-58248, …) with payload, root cause, and bounty · read when matching your target to a known race class or citing precedent.

Related Skills & Chains

• hunt-business-logic — Race conditions are the "concurrency arm" of every business-logic state machine. Chain primitive: business logic (coupon/promo) + race-condition single-packet attack → coupon redeemed N times → direct financial loss.
• hunt-mfa-bypass — OTP-expiry windows and replay protection are classic race targets. Chain primitive: race + MFA-validate endpoint → bypass OTP expiry by submitting N concurrent validations within the validity window.
• hunt-ato — Race conditions on password reset, email change, and account creation enable persistent ATO. Chain primitive: race on email-change endpoint + atomic-update missing → swap victim email + read reset token before user notice.
• hunt-api-misconfig — Wallet/balance/credit endpoints without atomic UPDATE are double-spend candidates. Chain primitive: race + atomic-update missing → double-spend balance → withdraw N× user balance.
• security-arsenal — Load the Turbo Intruder single-packet template, h2.cl smuggling for atomic submit, and curl --next parallel multi-request patterns.
• triage-validation — Apply the Statistical-Sampling gate: a single anomalous response is noise; require 1 successful + N duplicate / over-quota / stale-state demonstrations with response screenshots before reporting.