[zdyn5]

Naive question: how is brute-force cracking still a thing in real-world systems? Aren’t there time-outs/bans for guessing wrong after like 3-5 guesses? How does one get the opportunity to try millions/billions/etc of times?

[tetha]

Offline vs online brute forcing, as I like to call it.

As others have said, if you have the hashes, you can brute force them offline and there won't be any limits on how fast it can go besides your algorithms and compute resources.

But even online, attackers can be pretty smart. For example, something we detected was an attacker rotating both through a bunch of accounts and a bunch of IP addresses. That way you never saw many incorrect login tries per account and IP in a timeframe. It's not millions/billions of tries, but it can get around naive limits per IP or per account and you need some SIEM tooling to detect that.

[stavros]

Modern KDF algorithms are designed to guard against offline attacks by massively increasing the cost per hash. Online or offline, brute forcing shouldn't be an issue nowadays.

Saying "there's no limit besides your resources" is basically saying "there's no limit besides the very real and insurmountable limit there is".

[Ellipsis753]

This is for cracking password _hashes_. Most websites won't store a user's plain-text password but will only store the hash of it. Then a hack/exploit might later reveal the website's password hashes. This program helps you turn the hash back into the original password. Assuming you have a hash already, you own the hash, so it's not possible for anyone to impose a rate limit on how quickly you can attempt to break it.

[Etheryte]

Databases get dumped, well, not all the time, but fairly often. See haveibeenpwned for example, they post a new breach once a week, if not more often [0].

[0] https://feeds.feedburner.com/HaveIBeenPwnedLatestBreaches

[fullspectrumdev]

HIBP even is basically tip of the iceberg in terms of how much data is floating around - Troy and his team only get the ones that are publicly leaked, or privately shared with them.

They also have historically had a backlog of data to process - leaked databases can be a pain to parse and turn into something usable.

[starmilk]

What you generally feed into password cracking software is hashes of passwords that you've found by listening on the network, dumping from memory, or obtained by chaining another vulnerability.

These are in a text file locally (offline), so there is no system that you are submitting hashes to for verification. It simply tries md5(your_password_guess) until it computes the same hash that you supplied.

This is oversimplified and you can replace md5 with any hash alg that you need, but i hope it makes it clear that guesses don't happen against the auth server.

[kemotep]

Well if not setup properly, it is possible to dump the Windows password hashes (and linux too).

You take that list of hashes, and copy to your password cracking rig, where it can run for a few days to see how many password hashes you can find a match for. Then once you have identified a password hash match, you now know an account password.

However, if things aren’t properly secured where an attacker can dump password hashes, they likely can utilize “pass the hash” style attacks as well where you don’t even need to know the password to be able to sign in as a user.

[px43]

Windows networks are notoriously bad about this. If you find yourself on a Windows network, either because you found an active ethernet jack in the lobby, or you get on the wifi, phishing, or you land on a citrix box or whatever, you can run a tool called Responder.

Windows machines on a network are constantly scanning around, looking for new devices, and when they find them, they like to see if they can access them so they show up in network manager or whatever. They do this by trying to log in. Obviously logging in with a password would be insecure, so they try to log in with a hash. Responder pretends to be any sort of server that a Windows machine would try to log in to, so right when you run it, all the nearby machines hand over their hashes.

Crack even one of those hashes, and now you can log in to Active Directory. This will let you get the full list of all users, permissions, groups, machines, and sessions, etc, and basically tell you exactly what you need to do to get anywhere you want (Bloodhound is the main tool people use for this).

That AD account also lets you dump all the SPNs (service accounts) on the network, and because Windows is Windows, of course that gives you something like 20-30 password hashes, many of which are almost certainly Domain Admins on the network.

Crack a Domain Admin account, and you can basically do whatever you want on the network, including doing a dcsync, which is normally used to back up a domain controller, but also dumps every account and NTLM hash straight into your lap. These hashes can be used with pass-the-hash to impersonate any account, or you can just crack them and basically have free access to the network for the rest of your life.

The entire security of Windows networks is based on the premise that password crackers don't exist, which is why they have been fundamentally fucked for decades, and there's zero chance that any of this will ever get fixed.

[coffeeri]

You don't need to do this online in many cases. For instance, the hash of WPA-secured Wi-Fi networks can be captured during the handshake of other devices.

[einarfd]

If you manage to steal the file with the hashed passwords. Then none of that makes a difference.

[zdyn5]

Thanks everyone for these informative answers!