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Stop Using JWTs

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Re: Stop Using JWTs

#11

Post by tracker1 »

ApolloFortyNine wrote: post #8

This links to some other blog post for the bulk of it's 'why', and that blog post mostly seems to be annoyed about "You cannot invalidate individual JWT tokens". Which every time I've implemented, the general guideline is to check for invalidated nonces somewhere. Which resolves that random blog posts second point too. >The JWT specification itself is not trusted by security experts. This feels like it needs more evi…

Yeah... some early implementations just allowed for any authority to be set in the header and trusted it... that's of course wrong from the start... if you only allow for trusted or "known" authorities a lot of the contextual concerns become non-concerns.

Beyond this, you can make shorter lived JWTs just fine in the browser and have the agents self-update. If you use Azure Entra or a number of other providers it works this way in practice... you keep your JWTs relatively short lived (5-15m) and can even check for jti revokation.

JWTs are incredibly useful for separating/reusing an access authority from your applications/api systems. You shift the attack surface and do it in a way that can be trusted. We use PPK for lots of things, including SSH all over the world. No, I wouldn't use shared secrets and I wouldn't use long lived tokens... but short lived, ppk signed tokens from verified/known sources are generally fine.

For that matter, it's often API keys that are really problematic. Just had to implement them... for me, the API key presents as a Bearer token as well, but there's a short "sak." prefix then an identity part (base64url uuid bytes) followed by a secret as base64url bytes... in the database is the uuid and a passphrase level salt+hash from the secret.. so the api key generated should be treated as a secret and is one-way to the database, so a db breach doesn't breach auth.

Even then, an API key leak is far mroe likely than a problem with a well implemented JWT solution.

Re: Stop Using JWTs

#12

Post by vova_hn2 »

One of the articles that TFA links to [0] contains the following paragraphs:

> And there are more security problems. Unlike sessions - which can be invalidated by the server whenever it feels like it - individual stateless JWT tokens cannot be invalidated. By design, they will be valid until they expire, no matter what happens. This means that you cannot, for example, invalidate the session of an attacker after detecting a compromise. You also cannot invalidate old sessions when a user changes their password.

> You are essentially powerless, and cannot 'kill' a session without building complex (and stateful!) infrastructure to explicitly detect and reject them, defeating the entire point of using stateless JWT tokens to begin with.

I'm not sure that this is entirely true. Typically, the total number of non-expired issued tokens is much higher than the number of invalidated unexpired tokens. Therefore, if you store only invalidated tokens and delete them when they get expired, you can significantly reduce the amount of required storage and the cost of lookup.

Although, in any real application the performance gains will be minuscule (compared to the cost of, you know, everything else. Auth is just a small part) and probably not worth the extra complexity.

[0] "Stop using JWT for sessions" - http://cryto.net/~joepie91/blog/2016/06/13/stop-using-jwt-fo...

Re: Stop Using JWTs

#13

Post by kyrra »

solatic wrote: post #3

Necessary qualifier: for browser-based user sessions. Plenty of good uses for JWTs for service-to-service communication. edit: I read some of the linked stuff, e.g. https://paragonie.com/blog/2017/03/jwt-json-web-tokens-is-ba... . Please, if JWTs are such a horrifically insecure standard, go ahead and publish your means for hacking AWS STS's AssumeRoleWithWebIdentity , or don't publish and just exploit it by launchin…

JWT used to be bad due to libraries with poor defaults. Downgrade attacks were fairly common a number of years ago.

Since most of the common libraries across all languages have gotten more sane defaults, it actually is pretty secure nowadays.

Re: Stop Using JWTs

#14

Post by wccrawford »

szmarczak wrote: post #10

No need to stop. The XSS argument also applies when using cookies. JWTs are just tokens like session data but in JSON format. What format you choose to go with doesn't matter. You can keep storing JWTs in local storage and still be secure. Discord removes it on page load and restores it when the tab is closed. Also if your website is susceptible to XSS, skill issue, exactly like in the case of SQL injections. That wo…

I think anything can be abused, and too many people don't have a security-first mindset.

One of the advantages of JWTs is that you don't have to check your database or filesystem to make sure the the user is valid and logged in. All that data is in the JWT. If it's just a static page, it doesn't need to hit any data.

The problem then comes that some developers think that makes it secure, and don't check the database for revocation before doing anything with the account. Especially not for giving out private data. They might check before changing any data.

I think it's a really neat idea that is far too easy to mishandle and create a bad situation. It can save a lot of bandwidth and CPU cycles if you have a lot of non-interactive pages and all you need to know is whether to show that the user is logged in or not. But for actually doing anything, it's practically no better than a session cookie, and it's got a lot of foot-guns.

Re: Stop Using JWTs

#15

Post by Grollicus »

I'm right now adding rabbitmq for notification pushing to a website. Using JWT authentication to control where and what clients are allowed to read, with short lifetimes and regular token refresh.

I don't see another setup that comes close to the ease of setting this up - add an endpoint that provides jwt tokens to valid sessions, done. With user-individual permissions.

Re: Stop Using JWTs

#16

Post by RagingCactus »

solatic wrote: post #3

Necessary qualifier: for browser-based user sessions. Plenty of good uses for JWTs for service-to-service communication. edit: I read some of the linked stuff, e.g. https://paragonie.com/blog/2017/03/jwt-json-web-tokens-is-ba... . Please, if JWTs are such a horrifically insecure standard, go ahead and publish your means for hacking AWS STS's AssumeRoleWithWebIdentity , or don't publish and just exploit it by launchin…

> Necessary qualifier: for browser-based user sessions.

> Plenty of good uses for JWTs for service-to-service communication.

This is the sensible conclusion right there. I agree JWTs are the wrong tool for the use case of user sessions in the browser.

To give some more arguments:

All the signature and encryption stuff in JWTs is complex. While common JWT libraries have now mostly got their stuff together, this has not always been the case. There were plenty of libraries accepting the "none" algorithm [1] or allowing attackers to forge tokens by using a public key as a shared secret [2]. This is the direct result of the complexity criticized in the linked blog post.

JWTs also cannot do some stuff you want for user sessions. You can't invalidate them without keeping a revocation list somewhere. But if you have to check an identifier for revocation on every request you could just use an opaque session ID and look that up on every request instead! Sure, you can use short-lived tokens and refresh them all the time, but why bother with that for a typical application that has to keep some state anyway?

All that being said, I wholeheartedly agree that there are use cases in distributed systems and machine-to-machine communication where signed tokens can be useful. Just please don't confuse the two cases.

[1] https://nvd.nist.gov/vuln/detail/cve-2022-23540

[2] https://nvd.nist.gov/vuln/detail/CVE-2024-54150 (just a random example from googling, I don't know what library made this one infamous)

Re: Stop Using JWTs

#18

Post by jotato »

ApolloFortyNine wrote: post #8

This links to some other blog post for the bulk of it's 'why', and that blog post mostly seems to be annoyed about "You cannot invalidate individual JWT tokens". Which every time I've implemented, the general guideline is to check for invalidated nonces somewhere. Which resolves that random blog posts second point too. >The JWT specification itself is not trusted by security experts. This feels like it needs more evi…

> "You cannot invalidate individual JWT tokens". Which every time I've implemented, the general guideline is to check for invalidated nonces somewhere. Which resolves that random blog posts second point too.

100% agree. This is common sense to me and I'm always surprised to re-learn people don't do this

Re: Stop Using JWTs

#19

Post by nine_k »

RagingCactus wrote: post #16
solatic wrote: post #3

Necessary qualifier: for browser-based user sessions. Plenty of good uses for JWTs for service-to-service communication. edit: I read some of the linked stuff, e.g. https://paragonie.com/blog/2017/03/jwt-json-web-tokens-is-ba... . Please, if JWTs are such a horrifically insecure standard, go ahead and publish your means for hacking AWS STS's AssumeRoleWithWebIdentity , or don't publish and just exploit it by launchin…

> Necessary qualifier: for browser-based user sessions. > Plenty of good uses for JWTs for service-to-service communication. This is the sensible conclusion right there. I agree JWTs are the wrong tool for the use case of user sessions in the browser. To give some more arguments: All the signature and encryption stuff in JWTs is complex. While common JWT libraries have now mostly got their stuff together, this has no…

> if you have to check an identifier for revocation on every request you could just use an opaque session ID and look that up on every request instead!

One reason could be the size. A revocation list only needs to keep session IDs of recently logged-out sessions, for which the token's TTL hasn't yet expired. It may be a much smaller list than a list of every active session.

Also, a JWT (or a Macaroon, etc) can store a large amount of details about the session in a cryptographically secure, unforgeable way. This rids you of the necessity to store all that in your active session database, again cutting the size.

Re: Stop Using JWTs

#20

Post by hparadiz »

JWTs are for authenticating an already trusted system with another system.

Using them as the primary source of truth is an anti-pattern like the blog post is actually saying.

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