Re: [OAUTH-WG] Implementation questions around refresh token rotation

[Dave Tonge <[e-mail]>]

Hi Neil

 > refresh token rotation is better thought of as providing protection
against insecure token storage on the client

I agree with your reasoning - and that was more the intent of what I said.
We've seen refresh token rotation used for confidential clients that have
secure storage (i.e. are run in a data center not on a mobile device) and
it has caused problems with zero additional security benefits.

Dave


On Mon, 12 Oct 2020 at 08:57, Neil Madden <[e-mail]> wrote:

> I’m not sure I agree with this advice. Singling out private_key_jwt and
> tls_client_auth suggests that the problem is an attacker being able to
> eavesdrop on the refresh request itself and then replay it. But if they are
> able to do that then they can instead just steal the access tokens from the
> response.
>
> I think refresh token rotation is better thought of as providing
> protection against insecure token storage on the client (e.g. in browser
> localStorage). Both public and confidential clients are capable of creating
> secure connections with TLS, but we assume that confidential clients
> (regardless of auth mechanism) have access to secure storage - otherwise
> they shouldn’t be confidential clients in the first place.
>
> I think the same reasoning applies here too - if a client has insecure
> storage then an attacker could just steal the access tokens instead. But I
> think the difference is that an attacker is more likely to gain temporary
> access to local storage (e.g. when the user goes to the bathroom and leaves
> their device unlocked) than they are to gain temporary access to eavesdrop
> on a connection. The kind of vulnerabilities that allow eavesdropping tend
> to be repeatable so the attacker doesn’t need to steal a refresh token to
> ensure ongoing access, they can just steal the access tokens every time the
> client refreshes.
>
> That said, there are lots of vulnerabilities that would give an attacker
> repeatable access to the client’s local storage - e.g. XSS - so refresh
> token rotation only catches a subset of possible attacks.
>
> — Neil
>
> On 12 Oct 2020, at 05:43, Dave Tonge <[e-mail]> wrote:
>
> > Our goal is to prevent cases where we lose the ability to Refresh a
> Token due to transient issues (which have run the gamut from network
> problems to bad software updates on the AS side).
>
> We've seen this issue quite a bit and it's very frustrating. I would
> suggest that refresh token rotation is not used for confidential clients
> that authenticate with private_key_jwt or tls_client_auth.
>
> On Wed, 7 Oct 2020 at 00:57, Jeff Craig <jeffcraig=
> [e-mail]> wrote:
>
>> My experience is more from the Client side of the equation on this
>> problem, but I do have some thoughts. Our goal is to prevent cases where we
>> lose the ability to Refresh a Token due to transient issues (which have run
>> the gamut from network problems to bad software updates on the AS side).
>> Our use case also does all token handling server-side, so our threat model
>> is not the same as the mobile application you described. There is a clear
>> tradeoff in reducing user friction with additional authorization events,
>> and securing access.
>>
>> The recommendation my team typically gives people building Authorization
>> Servers with Refresh Token Rotation is to keep the old refresh token until
>> they see the new one (which means that there are generally two refresh
>> tokens valid at any point in time, an unfortunate trade-off). A more
>> difficult, but potentially plausible implementation would be to hold onto
>> the older Refresh Token until the newly issued Access Token is used (thus
>> implying the refresh was successful on both sides).
>>
>> We aren't trying to protect against multiple in-flight refreshes though
>> (we've done a LOT of work to attempt to remove that possibility in a
>> globally consistent manner), we're trying to protect against a network
>> interruption that prevents the first use of R1, so our assumption is that
>> R2.1 was completely lost, and only R2.2 matters moving forward. Meaning: R1
>> is sent, A/R2.1 is dropped in flight, R1 is sent again, A/R2.2 is returned
>> and stored. Since R1 was seen a second time, we recommend that R2.1 be
>> ignored in future. Next refresh will use R2.2, at which point R1 should
>> never be seen again.
>>
>> The biggest issue that I see with a time-based grace period is that for
>> many offline tasks, a single refresh failure may be ignored by the client,
>> and it could be hours before the second refresh attempt using the older
>> refresh token is made (depending on time of day and what these requests are
>> being used for), making the grace period low value in that case.
>>
>> On Tue, Oct 6, 2020 at 5:28 PM <vittorio.bertocci=
>> [e-mail]> wrote:
>>
>>> Hey Aaron,
>>>
>>> Auth0 does offer a configurable grace period, during which the
>>> “preceding” token can be reused.
>>>
>>> I am not 100% sure what we do in the exact scenario you described, and I
>>> will double check for you, but here’s my intuition.
>>>
>>>
>>>
>>> The operation redeem(RT_n) should result in AT, RT_n+1. The grace period
>>> just extends the time in which the operation can occur, but every operation
>>> should be idempotent. All repeats of that operation within the grace period
>>> should have the same result, which means that every resulting RT is a
>>> representative of the RT_n+1 class, hence all valid at the same time. After
>>> the grace period elapses, RT_n is invalid, and that’s it.
>>>
>>> So, in your example I would consider RT1.1 and RT1.2 as equivalent, as
>>> they are both representatives of the RT_n+1 equivalence class.
>>>
>>>
>>>
>>> It would be very hard to do otherwise, given that network operations
>>> aren’t guaranteed to be concluded in the order they were executed without
>>> semaphores, and above all the network failures the grace period is designed
>>> to handle can apply to any of the requests, regardless of the order.
>>>
>>>
>>>
>>> *From:* OAuth <[e-mail]> *On Behalf Of *Aaron Parecki
>>> *Sent:* Tuesday, October 6, 2020 3:06 PM
>>> *To:* OAuth WG <[e-mail]>
>>> *Subject:* [OAUTH-WG] Implementation questions around refresh token
>>> rotation
>>>
>>>
>>>
>>> Hi all, I have a couple questions for those of you who have implemented
>>> refresh token rotation...
>>>
>>>
>>>
>>> Have you included the option of a grace period on refresh token use,
>>> allowing multiple uses within some time window? I'm wondering because a
>>> grace period where a refresh token may be used more than once would work
>>> around the problem that has been brought up, of a mobile app accidentally
>>> using a refresh token more than once during normal operation because
>>> different threads are unable to coordinate between themselves. However that
>>> also kind of defeats the purpose since attacks within that grace period
>>> would be hard to detect. I'm looking for an idea of where people have
>>> landed on that issue in practice.
>>>
>>>
>>>
>>> If you have implemented a grace period, then how do you handle expiring
>>> the additional refresh tokens that have been granted? For example, if RT
>>> "R1" is used twice, resulting in new ATs "A1.1", "A1.2" and new RTs "R1.1"
>>> and "R1.2", what happens if "R1.2" is then later used? Would you invalidate
>>> "R1.1" at that point? If so, why, and if not, why not?
>>>
>>>
>>>
>>> It would be most interesting to hear practical experience from people
>>> who have already built refresh token rotation into a system.
>>>
>>>
>>>
>>> Thanks!
>>>
>>>
>>> ---
>>>
>>> Aaron Parecki
>>>
>>> https://aaronparecki.com
>>>
>>>
>>> _______________________________________________
>>> OAuth mailing list
>>> [e-mail]
>>> https://www.ietf.org/mailman/listinfo/oauth
>>>
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>
>
> --
> Dave Tonge
>
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Moneyhub Enterprise is a trading style of Moneyhub Financial Technology 
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Authority ("FCA"). Moneyhub Financial Technology is entered on the 
Financial Services Register (FRN 809360) at https://register.fca.org.uk/ 
<https://register.fca.org.uk/>. Moneyhub Financial Technology is registered 
in England & Wales, company registration number 06909772. Moneyhub 
Financial Technology Limited 2020 © Moneyhub Enterprise, Regus Building, 
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