Mmcp.market

hunt-race-condition skill

by elementalsouls·elementalsouls/Claude-BugHunter·4.7k stars·MIT

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.

A100/100content scan

Is the hunt-race-condition skill safe?

Clean: nothing in its files matched our rules. We read 1 file in the folder on 2026-09-28.

No findings.

Install the hunt-race-condition skill

A skill is a folder. Copy it into your agent's skills folder and the agent loads it when the task matches its description. 

git clone --depth 1 https://github.com/elementalsouls/Claude-BugHunter.git /tmp/Claude-BugHunter
mkdir -p ~/.claude/skills
cp -r /tmp/Claude-BugHunter/skills/hunt-race-condition ~/.claude/skills/hunt-race-condition
available in every project

In the Claude apps, zip the folder and upload it from the Skills settings. The folder on GitHub

The instructions your agent would load

SKILL.md as published, without the frontmatter. Read it on GitHub

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:

double-spend a coupon/gift-card, exceed a one-per-user quota). Success = ≥2 of the N return 2xx.

  • Identical-copies race — fire N IDENTICAL copies of one request at once (limit-overrun:

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):

  • Different-requests race (partial construction) — fire a LIST of DIFFERENT requests in one
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:

  • Monetary/credit systems — double-spending gift cards, coupons, referral bonuses, promotional credits, wallet balances
  • Vote/reputation manipulation — upvoting the same content multiple times, gaming leaderboards or trending algorithms
  • Account limits bypass — exceeding free-tier quotas, bypassing "one per user" restrictions on invites, trial activations, or API key generation
  • Privilege escalation — racing role assignment or permission checks during user creation/upgrade flows
  • Deletion bypass — reading or exfiltrating data during a narrow window between "marked for deletion" and "actually deleted"
  • Payment flows — charging a card once but receiving multiple fulfillments

Best-paying asset types: Fintech apps, SaaS platforms with credit/subscription models, social platforms with reputation systems, e-commerce checkout flows, OAuth/SSO token endpoints.

Attack Surface Signals

URL Patterns

/vote, /upvote, /like, /favorite
/redeem, /apply-coupon, /use-code, /claim
/purchase, /checkout, /confirm-order, /pay
/transfer, /withdraw, /send-money
/invite, /referral, /accept-invite
/upgrade, /activate, /trial
/delete, /deactivate, /cancel
/follow, /subscribe

Response Headers That Signal Race-Prone Backends

X-RateLimit-*        # rate limiting exists, but may not be atomic
X-Request-Id         # each request independently tracked
No Cache-Control     # stateful ops not idempotent

JavaScript Patterns to Grep

// Single-use action buttons with client-side disable
button.disabled = true
$('#btn').prop('disabled', true)
// Optimistic UI updates (state set before server confirms)
setState({ used: true })
// Sequential async calls without locking
await useVoucher(); await deductBalance();

Tech Stack Signals

  • Ruby on Rails without with_lock / lock! — ActiveRecord doesn't lock by default
  • Node.js with async/await chains — non-atomic DB reads then writes
  • PHP without SELECT ... FOR UPDATE — common in legacy codebases
  • Microservices — inter-service calls introduce natural TOCTOU windows
  • Redis counters without Lua scripts or INCR atomicity checks
  • Message queues — idempotency keys often missing

Step-by-Step Hunting Methodology

  1. Enumerate one-time or limited-use actions — Map every endpoint that enforces a "once per user", "limited quantity", or "deduct balance" constraint. These are your primary targets.
  1. Understand the state machine — For each target action, identify: (a) what state is read, (b) what state is written, (c) what validation sits between read and write. The gap between read and write is your window.
  1. Capture a clean baseline request — Perform the action once legitimately with Burp Suite intercepting. Confirm you get the expected single-use behavior (e.g., coupon marked used, vote counted once).
  1. Set up parallel request tooling — Use one of:
  • Burp Suite Repeater → "Send group in parallel" (Turbo Intruder for HTTP/2 single-packet attacks)
  • Turbo Intruder with engine=Engine.BURP2 for last-byte sync
  • curl with & backgrounding
  • Python threading or asyncio with pre-built connections
  1. Execute the race — Send 10–50 identical requests simultaneously. Key technique: pre-connect and buffer all requests, release the final byte of all simultaneously (single-packet attack when HTTP/2 is available).
  1. Analyze responses — Look for:
  • Multiple 200 OK where only one should succeed
  • Duplicate success messages
  • Database constraint errors (signals the race worked but hit the last-line-of-defense)
  • Inconsistent response times (one fast, rest slow = serialized; all same speed = parallel processing)
  1. Verify the effect — Check the actual state: Was the credit applied twice? Did the vote count increment multiple times? Is the coupon still marked unused despite two successes?
  1. Determine exploitability window — Re-run with decreasing parallelism (5 requests, 3 requests, 2 requests) to understand how tight the window is and reliability of exploitation.
  1. Test across account types — Sometimes the race only works for new accounts, specific subscription tiers, or under specific server load. Test varied conditions.
  1. Document reproducibility — Record exact timing, number of parallel requests needed, and success rate across 5 independent attempts before reporting.

Payload & Detection Patterns

Turbo Intruder — Basic Parallel Race

# turbo_intruder_race.py
def queueRequests(target, wordlists):
    engine = RequestEngine(endpoint=target.endpoint,
                           concurrentConnections=1,
                           engine=Engine.BURP2)  # HTTP/2 single-packet
    for i in range(20):
        engine.queue(target.req, gate='race1')
    engine.openGate('race1')

def handleResponse(req, interesting):
    if '200' in req.status:
        table.add(req)

curl — Parallel Requests (bash)

# Fire 15 simultaneous vote/redeem requests
for i in $(seq 1 15); do
  curl -s -o /dev/null -w "%{http_code}\n" \
    -X POST "https://target.com/api/vote" \
    -H "Cookie: session=YOUR_SESSION" \
    -H "Content-Type: application/json" \
    -d '{"report_id": "12345", "vote": "up"}' &
done
wait

Python asyncio Race

import asyncio, aiohttp

async def race_request(session, url, payload, headers):
    async with session.post(url, json=payload, headers=headers) as r:
        return await r.text()

async def main():
    url = "https://target.com/redeem"
    payload = {"code": "GIFT50"}
    headers = {"Cookie": "session=XXXXX"}
    
    async with aiohttp.ClientSession() as session:
        tasks = [race_request(session, url, payload, headers) for _ in range(20)]
        results = await asyncio.gather(*tasks)
    
    for r in results:
        print(r[:100])  # print first 100 chars of each response

asyncio.run(main())

Grep Patterns for Source Code Auditing

# Look for read-then-write without locking
grep -rn "find_by\|where.*first" --include="*.rb" | grep -v "lock"
grep -rn "SELECT.*WHERE" --include="*.php" | grep -v "FOR UPDATE"

# JavaScript async without atomicity
grep -rn "await.*get\|await.*find" --include="*.js" -A2 | grep "await.*update\|await.*save"

# Python Django ORM without select_for_update
grep -rn "\.get(\|\.filter(" --include="*.py" | grep -v "select_for_update"

HTTP/2 Single-Packet Check

# Verify target supports HTTP/2 (prerequisite for single-packet attack)
curl -sI --http2 https://target.com | grep -i "HTTP/2\|h2"

Common Root Causes

  1. Check-Then-Act without atomic operations — Developer reads state (if voucher.used == false), then writes state (voucher.update(used: true)) in two separate database operations. Any thread can read the same "unused" state before either writes.
  1. Missing database-level locking — Using ORM methods like find or filter instead of SELECT ... FOR UPDATE. The fix is one line but developers don't think about concurrency.
  1. Optimistic concurrency without version checking — Systems increment counters or mark records without checking if the record changed since it was read.
  1. Microservice TOCTOU — Service A validates eligibility, Service B executes the action. No shared atomic transaction spans both services.
  1. Client-side "protection" — Developers disable the button in JavaScript after first click, assuming that prevents duplicate submissions. Server-side logic is never hardened.
  1. Counter increments outside transactions — votes_count += 1; save() instead of an atomic SQL UPDATE SET votes = votes + 1 WHERE id = ?.
  1. Async background jobs — Eligibility checked synchronously, fulfillment done asynchronously. A second request passes the check before the first job completes.
  1. Caching without invalidation — Cached "has user voted?" check returns stale false during a cache miss window when the first write hasn't propagated yet.

Bypass Techniques

What Defenders Implement (and How to Bypass)

Defense: Per-user rate limiting

  • Bypass: Rate limits are checked before the action executes. Send requests simultaneously — all pass the rate-limit check before any is counted.

Defense: Idempotency keys / unique request tokens

  • Bypass: If the server generates or reuses the token, try sending parallel requests without the token. Or check if the uniqueness check itself has a race window.

More skills from elementalsouls/Claude-BugHunter

  • Aapk-redteam-pipelineEnd-to-end Android APK red-team pipeline — automated APK acquisition (Play Store + apkpure + apkmirror fallback), jadx decompilation, secret/URL/JWT/Firebase grep, pinned-cert extraction, exported-component enumeration, Frida runtime instrumentation templates, intent-injection probes. Built from an authorized external red-team engagement where 7 APKs were pulled manually, 4 download attempts truncated, and a hardcoded JWT + 30 internal API endpoints were recovered from one of the apps. Use when target has a mobile app catalogue (Play Store developer page), when you find an APK URL hosted on a web server, or when post-recon mentions "mobile app" in scope.
  • Fbb-local-toolkitLocal-tooling companion to the bug-bounty orchestrator — carries the SAME complete bug-bounty workflow, but reach for THIS variant when you also need to resolve where tools, wordlists, and clones are installed on the local machine (jhaddix, SecLists, trufflehog, ffuf, dalfox, ghauri); for pure orchestration/routing use the bug-bounty skill. Workflow it covers — recon (subdomain enumeration, asset discovery, fingerprinting, HackerOne scope, source code audit), pre-hunt learning (disclosed reports, tech stack research, mind maps, threat modeling), vulnerability hunting (IDOR, SSRF, XSS, auth bypass, CSRF, race conditions, SQLi, XXE, file upload, business logic, GraphQL, HTTP smuggling, cache poisoning, OAuth, timing side-channels, OIDC, SSTI, subdomain takeover, cloud misconfig, ATO chains, agentic AI), LLM/AI security testing (chatbot IDOR, prompt injection, indirect injection, ASCII smuggling, exfil channels, RCE via code tools, system prompt extraction, ASI01-ASI10), A-to-B bug chaining (IDOR→auth bypass, SSRF→cloud metadata, XSS→ATO, open redirect→OAuth theft, S3→bundle→secret→OAuth), bypass tables (SSRF IP bypass, open redirect bypass, file upload bypass), language-specific grep (JS prototype pollution, Python pickle, PHP type juggling, Go template.HTML, Ruby YAML.load, Rust unwrap), and reporting (7-Question Gate, 4 validation gates, human-tone writing, templates by vuln class, CVSS 3.1, PoC generation, always-rejected list, conditional chain table, submission checklist). Use when you need the local install path of a tool / wordlist / clone for a hunt, or as the full-workflow variant when operating from this local toolkit; for general routing use the bug-bounty skill. 中文触发词：漏洞赏金、安全测试、渗透测试、漏洞挖掘、信息收集、子域名枚举、XSS测试、SQL注入、SSRF、安全审计、漏洞报告
  • Abb-methodologyUse at the START of any bug bounty hunting session, when switching targets, or when feeling lost about what to do next. Master orchestrator that combines the 5-phase non-linear hunting workflow with the critical thinking framework (developer psychology, anomaly detection, What-If experiments). Routes to all other skills based on current hunting phase. Also use when asking "what should I do next" or "where am I in the process."
  • Fbug-bountyComplete bug bounty workflow — recon (subdomain enumeration, asset discovery, fingerprinting, HackerOne scope, source code audit), pre-hunt learning (disclosed reports, tech stack research, mind maps, threat modeling), vulnerability hunting (IDOR, SSRF, XSS, auth bypass, CSRF, race conditions, SQLi, XXE, file upload, business logic, GraphQL, HTTP smuggling, cache poisoning, OAuth, timing side-channels, OIDC, SSTI, subdomain takeover, cloud misconfig, ATO chains, agentic AI), LLM/AI security testing (chatbot IDOR, prompt injection, indirect injection, ASCII smuggling, exfil channels, RCE via code tools, system prompt extraction, ASI01-ASI10), A-to-B bug chaining (IDOR→auth bypass, SSRF→cloud metadata, XSS→ATO, open redirect→OAuth theft, S3→bundle→secret→OAuth), bypass tables (SSRF IP bypass, open redirect bypass, file upload bypass), language-specific grep (JS prototype pollution, Python pickle, PHP type juggling, Go template.HTML, Ruby YAML.load, Rust unwrap), and reporting (7-Question Gate, 4 validation gates, human-tone writing, templates by vuln class, CVSS 3.1, PoC generation, always-rejected list, conditional chain table, submission checklist). Use for ANY bug bounty task — starting a new target, doing recon, hunting specific vulns, auditing source code, testing AI features, validating findings, or writing reports. 中文触发词：漏洞赏金、安全测试、渗透测试、漏洞挖掘、信息收集、子域名枚举、XSS测试、SQL注入、SSRF、安全审计、漏洞报告
  • Abugcrowd-reportingBugcrowd-specific reporting tactics complementing report-writing: VRT category search-and-fallback strategy when no exact match exists, manual severity override when VRT defaults underrate impact, severity-request paragraph as first body section, OOS-clause rebuttal templates (rate limiting on auth-flow endpoints, debug-info framing, user-enumeration with sensitive PII, theoretical-issue counter), chained-finding cross-reference patterns, target selection for QA-vs-prod programs, researcher-side hygiene (Bugcrowdninja email alias, account state restoration, friendly-tester posture). Use when filing a Bugcrowd submission, when VRT default seems wrong, when triager closes as OOS or downgrades severity, when chaining linked submissions, or when scope distinguishes production from QA. Pairs with report-writing and triage-validation.
  • Acloud-iam-deepCloud IAM red-team attack chain across AWS, Azure, GCP — focused on EXTERNAL exploitation paths and post-credential-discovery privilege analysis. Covers IAM enumeration (aws iam, az role, gcloud iam), STS/AssumeRole chaining, Azure Managed Identity abuse (via SSRF/leak), GCP service account JSON abuse, IMDSv1/v2 attacks via SSRF, K8s ServiceAccount token privilege analysis once held (token discovery / cluster exposure is owned by hunt-k8s), role-trust-policy confused-deputy, cross-account assume-role enumeration, IAM privilege escalation patterns (24+ AWS, 8+ Azure, 6+ GCP), and AWS Cognito Identity Pool unauthenticated-role attack chain (GetId → GetCredentialsForIdentity → IAM role abuse). Built for the case where recon yields a credential (key, JSON, token) and you need to know what it grants and how to escalate. Use when an AWS key / Azure secret / GCP service account JSON / K8s SA token surfaces from a code repo, JS bundle, APK, breach corpus, or SSRF chain.
  • Centerprise-vpn-attackExternal SSL VPN / remote-access appliance attack matrix — Cisco ASA/AnyConnect, Fortinet FortiGate/FortiOS, Citrix NetScaler/ADC, Palo Alto GlobalProtect, Pulse Secure / Ivanti Connect Secure, SonicWall, F5 Big-IP. Covers version fingerprinting, CVE matrix (2018-2026), AAA backend identification, default credentials, configuration-disclosure paths, pre-auth RCE/SSRF/path-traversal exploits where applicable. Built from authorized-engagement Cisco ASA testing plus 2024-2026 enterprise VPN CVE landscape. Use whenever the target's perimeter exposes any SSL VPN appliance or remote-access gateway — these are the most common initial-access points in 2024-2026 actor TTPs.
  • Aevidence-hygieneEvidence-capture and PoC-redaction discipline for bug-bounty submissions: cookie redaction protocol (which fields to mask, Preview annotation / Burp panel hiding / DevTools workflow), PII black-bar discipline (what to mask in other-user data — names, emails, phones, faces — vs what is safe to leave — usernames, trace IDs, request bodies), HAR file sanitization (jq filters for Cookie/Set-Cookie/Authorization headers), Burp Repeater/Intruder screenshot hygiene (hide request body, show only Results table for rate-limit attacks), Chrome DevTools Console PoC patterns (credentials include so cookies are not echoed, labeled console.log), screenshot capture order, filename conventions, post-submission rotation hygiene. Use BEFORE any PoC screenshot, BEFORE attaching a HAR, or whenever preparing evidence with session cookies or other-user PII. Pairs with bugcrowd-reporting and report-writing.
  • Ahunt-api-misconfigHunt API security misconfiguration — mass assignment, prototype pollution, HTTP verb tampering. Mass assignment: send {is_admin:true, role:admin, verified:true} on profile/account/reset endpoints — server blindly applies. JWT signature/crypto forging (alg:none, key confusion, kid/jku) is owned by hunt-jwt-crypto; this skill covers only non-crypto JWT handling. Prototype pollution: __proto__ injection in JSON merge / Object.assign / lodash _.merge → polluted prototype reaches sink (RCE in Node, XSS in browser). HTTP verb: GET-bypass-CSRF, X-HTTP-Method-Override, TRACE enabled. Detection: API responses with extra fields, JWTs in headers (decode at jwt.io). CORS misconfiguration (reflect-any-origin, null origin, subdomain-regex bypass, postMessage) is owned by hunt-cors. Use when hunting API misconfigs, mass-assignment, prototype pollution (JWT crypto → hunt-jwt-crypto).
  • Ahunt-aspnetHunt ASP.NET-specific surface — ViewState deserialization (signed-only vs encrypted), machineKey recovery, dual-parser MAC-bypass anti-pattern, request-validator bypass, trace.axd/elmah.axd disclosure, load-balanced ViewState cross-node failures, SafeControl enumeration via reflection, customErrors mode=Off stack-trace leaks, classic Webforms .aspx/.asmx/.svc surface. Built for ASP.NET Webforms + WCF + SharePoint farms.
  • Ahunt-atoHunt account takeover taxonomy — 9 distinct paths to ATO, plus chains. Paths: (1) password reset flaws (host-header injection redirects token, predictable/numeric token, Referer leak, no-expiry/reuse), (2) email change without re-auth, (3) OAuth account-link CSRF, (4) MFA bypass (per hunt-mfa-bypass), (5) session fixation, (6) JWT manipulation (forge token to another identity; crypto details → hunt-jwt-crypto), (7) password change without step-up (chain with login timing/length oracle), (8) social-recovery / security-question brute-force, (9) SSO subdomain takeover at OAuth redirect_uri. Chains: cookie theft + password oracle + no step-up = persistent ATO; lax redirect_uri = auth-code theft; dangling-CNAME takeover at redirect_uri = ATO. Validate: demonstrate real takeover of test account B from attacker A's session; OOB/Collaborator confirm blind token-leak steps. Use when hunting ATO chains, testing password reset / email change / MFA / OAuth / session / JWT, or chaining primitives toward Critical.
  • Ahunt-auth-bypassHunting skill for auth bypass vulnerabilities. Built from 12 public bug bounty reports across SAML XSW / parser-differential (GitHub Enterprise CVE-2025-25291/25292), SAML signature stripping (Uber, Rocket.Chat, samlify CVE-2025-47949), SAML domain enforcement bypass via control characters (HackerOne 2024), partner-portal cross-IdP assertion reuse (Slack), WordPress XMLRPC bypassing SSO (Uber), JWT alg-confusion HS256/RS256 (Jitsi), JWT signature-validation skip (Linktree, Newspack), and token-audience confusion (Argo CD CVE-2023-22482). For standalone JWT signature/crypto forging (alg:none, key confusion, kid/jku) see hunt-jwt-crypto; this skill covers JWT only inside SSO/SAML/token-trust bypass chains. SAML assertion-layer attacks (XSW, comment injection, signature stripping, XXE-in-assertion) are owned by hunt-saml; this skill owns the broader cross-protocol auth-bypass taxonomy. Use when hunting auth bypass — see the Legacy-Protocol Matrix for branded-UI vs legacy-endpoint patterns.

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