What Is a Rainbow Table Attack? Explained Simply

Hey, if you’re the one in charge of keeping user accounts safe (whether it’s a small app or a big company), passwords are always a pain point. Weak ones get guessed, strong ones get reused, and even when you do everything right, hackers still have tricks.

One of their sneakiest and fastest moves is the rainbow table attack, an old-school method that can still crack millions of passwords in seconds if you’re not protected.

In this post, I’ll break down what a rainbow table actually is, how attackers build and use them, why they’re so dangerously quick, and the simple fixes (like salting) that make them completely useless. Let’s go.

How a Rainbow Table Password Attack Works

Hackers don’t save a hash for every possible password; that would take insane amounts of space. Instead, they play a smart trick; they create long chains. They start with a password like “abc123”, hash it, then turn that hash back into a different fake password, hash that one, and keep going for thousands of steps. They only save the very first password and the very last hash of each chain. One chain can cover millions of passwords, but it takes almost no storage. That’s the “rainbow” part—colorful chains that save space.

When they steal your database of hashed passwords, they take one of your hashes and run it through the same chain trick in reverse. If it lands on the end of one of their saved chains, they just replay the whole chain from the beginning until they hit your exact hash. Boom, there’s your real password. The whole thing takes seconds or minutes because all the hard work was done months ago.

Rainbow tables destroy weak or common passwords super fast, but only if the site didn’t use salt (a random string added to every password before hashing). With salt, every user gets a different hash even if they have the same password, and the pre-made rainbow table becomes useless. That’s why good sites do this now, but tons of old or poorly built systems still don’t. And that’s why rainbow tables are still winning fights today.

Rainbow Table Attack Examples

Real breaches show how bad this can get. In 2012, hackers stole 6.5 million LinkedIn passwords. LinkedIn was using unsalted SHA-1 hashes, so anyone with a rainbow table could crack millions of them in hours. People who had “123456” or “linkedinpassword” woke up to hacked accounts and their credentials used everywhere else.

A year later, Ubuntu Forums lost 1.8 million accounts stored with unsalted MD5. Days later, half the passwords were posted online because free tools like RainbowCrack made it that easy.

It still happens on smaller scales, too: old company Windows servers with unsalted hashes, cheap IoT cameras, random forums, any place that skipped salting becomes instant prey.

The main point is that no salt + leaked hashes equals game over in minutes. The fix is simple and has been around forever, yet plenty of systems still don’t use it.

How to Prevent Rainbow Table Attacks

Here’s how to protect your passwords and secure your system from dangerous rainbow table attacks.

1. Use long, random passwords (16+ characters, total nonsense). Let a password manager like Bitwarden or 1Password make and remember them for you.
2. If you’re a developer: always salt your hashes (add a unique random string to every password before hashing) and use slow algorithms like bcrypt, Argon2, or PBKDF2. It’s literally one or two lines of code in any modern language.
3. Turn on 2FA/MFA everywhere. Even if they get the password, they still can’t get in without your phone or key.
4. Keep your database encrypted, patched, and off the open internet. Slow down login attempts so brute-force dies too.
5. Bonus: go passwordless when possible (Apple/Google passkeys, YubiKey, etc.) — no password, no hash, no rainbow table.

Conclusion

That’s the whole story. Rainbow tables only win when someone gets lazy: no salt, weak passwords, no 2FA. Do the simple stuff right (salt your hashes, use long random passwords with a password manager, turn on two-factor), and this attack is dead in the water. Threats will keep coming, but these basics still stop most of them. Stay sharp and keep your stuff updated.