[yellowapple]

> It is generally a good practice to not expose your primary keys to the external world. This is especially important when you use sequential auto-incrementing identifiers with type integer or bigint since they are guessable.

What value would there be in preventing guessing? How would that even be possible if requests have to be authenticated in the first place?

I see this "best practice" advocated often, but to me it reeks of security theater. If an attacker is able to do anything useful with a guessed ID without being authenticated and authorized to do so, then something else has gone horribly, horribly, horribly wrong and that should be the focus of one's energy instead of adding needless complexity to the schema.

The only case I know of where this might be valuable is from a business intelligence standpoint, i.e. you don't want competitors to know how many customers you have. My sympathy for such concerns is quite honestly pretty low, and I highly doubt GitLab cares much about that.

In GitLab's case, I'm reasonably sure the decision to use id + iid is less driven by "we don't want people guessing internal IDs" and more driven by query performance needs.

[tetha]

> I see this "best practice" advocated often, but to me it reeks of security theater. If an attacker is able to do anything useful with a guessed ID without being authenticated and authorized to do so, then something else has gone horribly, horribly, horribly wrong and that should be the focus of one's energy instead of adding needless complexity to the schema.

Yes, but the ability to guess IDs can make this security issue horrible, or much much worse.

If you had such a vulnerability and you are exposing the users to UUIDs, now people have to guess UUIDs. Even a determined attacker will have a hard time doing that or they would need secondary sources to get the IDs. You have a data breach, but you most likely have time to address it and then you can assess the amount of data lost.

If you can just <seq 0 10000 | xargs -I ID curl service/ticket/ID> the security issue is instantly elevated onto a whole new level. Suddenly all data is leaked without further effort and we're looking at mandatory report to data protection agencies with a massive loss of data.

To me, this is one of these defense in depth things that should be useless. And it has no effect in many, many cases.

But there is truely horrid software out there that has been popped in exactly the described way.

[dijit]

Case in point, a recent security issue Gitlab experienced (CVE-2023-7028; arbitrary password reset by knowing one of the accounts associated mail addresses) was made worse by a feature of gitlab that few people know about; that the "userID" is associated with a meta/internal mail address.

This meant that people could send password resets for any user if they knew their userID. The mail format was like [e-mail] or something.

Since it's a safe bet that "user ID 1" is an admin user, someone weaponised this.

[plagiarist]

I've already resolved to never use Gitlab entirely on the basis of that CVE but that makes it worse.

Password resets should just never go to an email that hasn't been deliberately attached to an account by the account's owner, full stop. There should not be a code path where it is possible to send any such thing to arbitrary emails. And redirect emails should never be treated as account emails in any way.

[yellowapple]

Even without that auto-incrementing ID, there are plenty of other options for guessing valid email addresses to use with that exploit. For example, if you're able to figure out the format an organization uses for their email addresses (e.g. [e-mail]), and you're able to figure out who works at that org (via e.g. LinkedIn), then there's a very good chance you can reset passwords for, say, the company's CTO or other likely-highly-privileged users.

That is: this kind of proves my point. Removing autoincrementing IDs from the equation is of minimal benefit when things have already gone horribly horribly wrong like this. It's a little bit more work on the attacker's part, but not by anywhere near enough for such a "mitigation" to be of much practical benefit.

[s4i]

It’s mentioned in the article. It’s more to do with business intelligence than security. A simple auto-incrementing ID will reveal how many total records you have in a table and/or their growth rate.

> If you expose the issues table primary key id then when you create an issue in your project it will not start with 1 and you can easily guess how many issues exist in the GitLab.

[no-dr-onboard]

Business intelligence isn’t really applicable on the database level with guids..way too many abstraction layers down.

[coldtea]

>I see this "best practice" advocated often, but to me it reeks of security theater.

The idea of "security theater" is overplayed. Security can be (and should be) multilayered, it doesn't have to be all or nothing. So that, when they break a layer (say the authentication), they shouldn't automatically gain easy access to the others

>If an attacker is able to do anything useful with a guessed ID without being authenticated and authorized to do so, then something else has gone horribly, horribly, horribly wrong and that should be the focus of one's energy instead of adding needless complexity to the schema.

Sure. But by that time, it's will be game over if you don't also have the other layers in place.

The thing is that you can't anticipate any contigency. Bugs tend to not preannounce themselves, especially tricky nuanced bugs.

But when they do appear, and a user can "do [something] useful with an ID without being authenticated and authorized to do so" you'd be thanking all available Gods that you at least made the IDs not guassable - which would also give them also access to every user account on the system.

[yellowapple]

> Security can be (and should be) multilayered, it doesn't have to be all or nothing.

In this case the added layer is one of wet tissue paper, at best. Defense-in-depth is only effective when the different layers are actually somewhat secure in their own right.

It's like trying to argue that running encrypted data through ROT13 is worthwhile because "well it's another layer, right?".

> you'd be thanking all available Gods that you at least made the IDs not guassable - which would also give them also access to every user account on the system.

I wouldn't be thanking any gods, because no matter what those IDs look like, the only responsible thing in such a situation is to assume that an attacker does have access to every user account on the system. Moving from sequential IDs to something "hard" like UUIDs only delays the inevitable - and the extraordinarily narrow window in which that delay is actually relevant ain't worth considering in the grand scheme of things. Moving from sequential IDs to something like usernames ain't even really an improvement at all, but more of a tradeoff; yeah, you make life slightly harder for someone trying to target all users, but you also make life much easier for someone trying to target a specific user (since now the attacker can guess the username directly - say, based on other known accounts - instead of having to iterate through opaque IDs in the hopes of exposing said username).

[coldtea]

>I wouldn't be thanking any gods, because no matter what those IDs look like, the only responsible thing in such a situation is to assume that an attacker does have access to every user account on the system. Moving from sequential IDs to something "hard" like UUIDs only delays the inevitable*

Well, there's nothing "inevitable". It's a computer system, not the fullfilment of some prophecy.

You can have an attack vector giving you access to a layer, without guaranteed magic access to other layers.

But even if it "just delays the inevitable", that's a very good thing, as it can be time used to patch the issue.

Not to mention, any kind of cryptography just "delays the inevitable" too. With enough time it can be broken with brute force - might not even take millions of years, as we could get better at quantum computing in the next 50 or 100.

[yellowapple]

> But even if it "just delays the inevitable", that's a very good thing, as it can be time used to patch the issue.

My point is that in this case, the additional time is nowhere near sufficient to make much of a difference. This is especially true when you consider that an attacker could be probing URLs before finding an exploit, in which case that tiny delay between "exploit found" -> "all users compromised" shrinks to zero.

[metafunctor]

Bugs happen also in access control. Unguessable IDs make it much harder to exploit some of those bugs. Of course the focus should be on ensuring correct access control in the first place, but unguessable IDs can make the difference between a horrible disaster and a close call.

It's also possible to use auto-incrementing database IDs and encrypt them, if using UUIDs doesn't work for you. With appropriate software layers in place, encrypted IDs work more or less automatically.

[lordgrenville]

> The only case where this might be valuable is business intelligence

Nitpick: I would not call this "business intelligence" (which usually refers to internal use of the company's own data) but "competitive intelligence". https://en.wikipedia.org/wiki/Competitive_intelligence

[EE84M3i]

See also "German Tank Problem" https://en.m.wikipedia.org/wiki/German_tank_problem

[remus]

In general it's a defense-in-depth thing. You definitely shouldn't be relying on it, but as an attacker it just makes your life a bit harder if it's not straightforward to work out object IDs.

For example, imagine you're poking around a system that uses incrementing ints as public identifiers. Immediately, you can make a good guess that there's probably going to be some high privileged users with user_id=1..100 so you can start probing around those accounts. If you used UUIDs or similar then you're not leaking that info.

In gitlabs case this is much less relevant, and it's more fo a cosmetic thing.

[serial_dev]

> In gitlabs case this is much less relevant (...)

Why, though? GitLab is often self hosted, so being able to iterate through objects, like users, can be useful for an attacker.

[yellowapple]

In my experience self-hosted GitLabs are rarely publicly-accessible in the first place; they're usually behind some sort of VPN.

As for an attacker being able to iterate through users, if that information is supposed to be private, and yet an attacker is getting anything other than a 404, then that's a problem in and of itself and my energy would be better spent fixing that.

[Anon1096]

This is again a defense in depth thing. In the age of WFH, cracking a corporate VPN is really not that difficult. If you can make an attacker's life harder for low cost you should do it just in case.

[yellowapple]

Except you ain't really putting up a meaningful obstacle against an attacker here. Compared to the typical effort of cracking a corporate VPN, brute-forcing IDs is downright trivial.

Like I said elsewhere: it's like calling ROT13 "defense in depth".

[remus]

You're right, fair point.

[worksonmine]

> What value would there be in preventing guessing?

It prevents enumeration, which may or may not be a problem depending on the data. If you want to build a database of user profiles it's much easier with incremental IDs than UUID.

It is at least a data leak but can be a security issue. Imagine a server doing wrong password correctly returning "invalid username OR password" to prevent enumeration. If you can still crawl all IDs and figure out if someone has an account that way it helps filter out what username and password combinations to try from previous leaks.

Hackers are creative and security is never about any single protection.

[yellowapple]

> If you can still crawl all IDs and figure out if someone has an account that way it helps filter out what username and password combinations to try from previous leaks.

Right, but like I suggested above, if you're able to get any response other than a 404 for an ID other than one you're authorized to access, then that in and of itself is a severe issue. So is being able to log in with that ID instead of an actual username.

Hackers are indeed creative, but they ain't wizards. There are countless other things that would need to go horribly horribly wrong for an autoincrementing ID to be useful in an attack, and the lack of autoincrementing IDs doesn't really do much in practice to hinder an attacker once those things have gone horribly, horribly wrong.

I can think of maybe one exception to this, and that's with e-commerce sites providing guest users with URLs to their order/shipping information after checkout. Even this is straightforward to mitigate (e.g. by generating a random token for each order and requiring it as a URL parameter), and is entirely inapplicable to something like GitLab.

[worksonmine]

> Right, but like I suggested above, if you're able to get any response other than a 404 for an ID other than one you're authorized to access, then that in and of itself is a severe issue. So is being able to log in with that ID instead of an actual username.

You're missing the point and you're not thinking like a hacker yet. It's not about the ID itself or even private profiles, but the fact that you can build a database of all users with a simple loop. For example your profile here is '/user?id=yellowapple' not '/user?id=1337'.

If it was the latter I could build a list of usernames by testing all IDs. Then I would cross-reference those usernames to previous leaks to know what passwords to test. And hacking an account is not the only use of such an exploit, just extracting all items from a competitors database is enough in some cases. It all depends on the type data and what business value it has. Sometimes an incrementing ID is perfectly fine, but it's more difficult to shard across services so I usually default to UUID anyway except when I really want an incrementing ID.

Most of the time things don't have to go "horribly horribly wrong" to get exploited. It's more common to be many simple unimportant holes cleverly combined.

The username can still always be checked for existence on the sign-up step, and there aren't many ways of protecting from that. But it's easier to rate-limit sign-ups (as one should anyway) than viewing public profiles.

Do you leave your windows open when you leave from home just because the burglar can kick the front door in instead? It's the same principle.

[yellowapple]

> Do you leave your windows open when you leave from home just because the burglar can kick the front door in instead?

Yes (or at least: I ain't terribly worried if I do forget to close the windows before leaving), because the likelihood of a burglar climbing up multiple floors to target my apartment's windows is far lower than the likelihood of the burglar breaking through my front door.

But I digress...

> You're missing the point and you're not thinking like a hacker yet.

I'd say the same about you. To a hacker who's sufficiently motivated to go through all those steps you describe, a lack of publicly-known autoincremented IDs is hardly an obstacle. It might deter the average script kiddie or botnet, but only for as long as they're unwilling to rewrite their scripts to iterate over alphanumerics instead of just numerics, and they ain't the ones performing attacks like you describe in the first place.

> For example your profile here is '/user?id=yellowapple' not '/user?id=1337'.

In either case that's public info, and it's straightforward to build a list of at least some subset of Hacker News users by other means (e.g. scraping comments/posts - which, mind you, are sequential IDs AFAICT). Yes, it's slightly more difficult than looping over user IDs directly, but not by a significant enough factor to be a worthwhile security mitigation, even in depth.

Unless someone like @dang feels inclined to correct me on this, I'm reasonably sure the decision to use usernames instead of internal IDs in HN profile URLs has very little to do with this particular "mitigation" and everything to do with convenience (and I wouldn't be all that surprised if the username is the primary key in the first place). '/user?id=worksonmine' is much easier to remember than '/user?id=8675309', be it for HN or for any other social network / forum / etc.

> Sometimes an incrementing ID is perfectly fine, but it's more difficult to shard across services so I usually default to UUID anyway except when I really want an incrementing ID.

Sharding is indeed a much more valid reason to refrain from autoincrementing IDs, publicly-known or otherwise.

[worksonmine]

> multiple floors

But not if you lived on the ground floor I assume?

> iterate over alphanumerics instead of just numerics

Why would you suggest another sequential ID as a solution to a sequential ID? I didn't, UUIDs have decent entropy and are not viable to brute force. Don't bastardize my point just to make a response.

> I'm reasonably sure the decision to use usernames instead of internal IDs in HN profile URLs has very little to do with this particular "mitigation" and everything to do with convenience

It wasn't intended as an audit of HN, I was holding your hand when walking you through an example and chose the site we're on. I missed my mark and I don't think a third attempt will do much difference when you're trying so hard not to get it. If you someday have public data you don't want a competitor to enumerate you'll know the solution exists.

[yellowapple]

> But not if you lived on the ground floor I assume?

Still wouldn't make much of a difference when my windows are trivial to break into even when closed.

> Why would you suggest another sequential ID

I didn't.

> UUIDs have decent entropy and are not viable to brute force.

They're 128 bits (for UUIDv4 specifically; other varieties in common use are less random). That's a pretty good amount of entropy, but far from insurmountable.

And you don't even need to brute-force anything; if these IDs are public, then they're almost certainly being used elsewhere, wherein they can be captured. There's also nothing stopping an attacker from probing IDs ahead of time, prior to an exploit being found. The mitigations to these issues are applicable no matter the format or size of the IDs in question.

And this is assuming the attacker cares about the specific case of attacking all users. If the attacker is targeting a specific user, or just wants to attack the first user one finds, then none of that entropy matters in the slightest.

Put simply: there are enough holes in the "random IDs are a meaningful security measure" argument for it to work well as a strainer for my pasta.

> when you're trying so hard not to get it

Now ain't that the pot calling the kettle black.

> If you someday have public data you don't want a competitor to enumerate you'll know the solution exists.

If I don't want a competitor to enumerate it then I wouldn't make the data public in the first place. Kinda hard to enumerate things when the only result of attempting to access them is a 404.

[JimBlackwood]

I follow this best practice, there’s a few reasons why I do this. It doesn’t have to do with using a guessed primary ID for some sort of privilege escalation, though. It has more to do with not leaking any company information.

When I worked for an e-commerce company, one of our biggest competitors used an auto-incrementing integer as primary key on their “orders” table. Yeah… You can figure out how this was used. Not very smart by them, extremely useful for my employer. Neither of these will allow security holes or leak customer info/payment info, but you’d still rather not leak this.

[tomnipotent]

> extremely useful for my employer.

I've been in these shoes before, and finding this information doesn't help you as an executive or leader make any better decisions than you could have before you had the data. No important decision is going to be swayed by something like this, and any decision that is probably wasn't important.

Knowing how many orders is placed isn't so useful without average order value or items per cart, and the same is true for many other kinds of data gleamed from this method.

[JimBlackwood]

That’s not correct. Not every market is the same in it’s dynamics.

Yes, most of the time that information was purely insightful and was simply monitored. However, at some moments it definitely drove important decisions.

[tomnipotent]

Like what?

What's going to change how a team develops (physical) products? What's a merchandiser or buyer going to learn that influences how they spend millions of dollars or deal with X weeks-on-hand of existing inventory? What's an operations manager going to learn that improves their ability to warehouse and ship product? How's marketing going to change their strategy around segmentation or channel distribution? What's a CEO going to learn that changes what departments or activities they want to invest in?

At best you get a few little tidbits of data you can include in presentations or board decks, but nothing that's going to influence critical decisions on how money is getting spent to get the job done or how time is getting allocated to projects. Worst case you have a inexperienced CEO that's chasing rather than leading, and just end up copying superficial aspects of your competitors without the context or understanding of why they did what they did.

I've called up execs at competitors and had friendly chats that revealed more about their business in 30 minutes than you could possibly find out through this "method".

[kehers]

One good argument I found [^1] about not exposing primary keys is that primary keys may change (during system/db change) and you want to ensure users have a consistent way of accessing data.

[^1]: https://softwareengineering.stackexchange.com/questions/2183...

[dalore]

It's also exposes your growth metrics. When using sequential id's one can tell how many users you have, how many users a month you are getting and all sorts of useful stuff that you probably don't want to expose.

It's how the British worked out how many tanks the German army had.

[SkyMarshal]

> This is especially important when you use sequential auto-incrementing identifiers with type integer or bigint since they are guessable.

I thought we had long since moved past that to GUIDs or UUIDs for primary keys. Then if you still need some kind of sequential numbering that has meaning in relation to the other fields, make a separate column for that.

[sgarland]

Except now people are coming back around, because they’re realizing (as the article mentions) that UUID PKs come with enormous performance costs. In fairness, any non-k-sortable ID will suffer the same fate, but UUIDs are the most common of the bunch.

[strzibny]

Whether you think it's a real problem or not, if you want to solve it somehow, I compiled the current options one have in Rails apps:

https://nts.strzibny.name/alternative-bigint-id-identifiers-...

[cyberfart]

There are also reasons outside infosec concerns. For example where such PKs would be directly related to your revenue, such as orders in an e-commerce platform. You wouldn't want competitors to have an estimate of your daily volume, that kind of thing.

[mnahkies]

It can be really handy for scraping/archiving websites if they're kind enough to use a guessable id

[heax]

It really depends but useful knowledege can be derived from this. If user accounts use sequential ids the id 1 is most likely the admin account that is created as first user.