RFR: 8270137: Kerberos Credential Retrieval from Cache not Working in Cross-Realm Setup

Martin Balao mbalao at openjdk.java.net
Tue Aug 10 13:48:31 UTC 2021


On Mon, 9 Aug 2021 19:54:21 GMT, Weijun Wang <weijun at openjdk.org> wrote:

>> I'd like to propose a fix for JDK-8270137 [1].
>> 
>> This bug is triggered when using a previously stored referral ticket (in the Referrals Cache) at the moment of following a S4U2Proxy cross-realm referral. The mistakenly-used referral ticket matched the client and service names but it was obtained as a result of a non-S4U2Proxy request. In fact, it was the middle service that got it while trying to determine the backend service realm in a previous S4U2Proxy communication. The mistakenly-used referral ticket was not bind to the impersonated user (in other words, it was not obtained attaching the user's TGS as part of a S4U2Proxy request) and, thus, must not be used.
>> 
>> Even when one possible approach to fix this issue could be to be more selective at the moment of getting referral tickets from the Cache (that is: do not get anything from the Cache if it's for a S4U2Proxy request), I decided to go one step further and enhance the Referrals Cache. With this enhancement, we add more information to the stored referral tickets such as a footprint of the TGS (in the case of S4U2Proxy requests) or the user principal (in the case of S4U2Self requests). We now allow to store S4U2Proxy and S4U2Self referrals tickets but those will be re-used only if there is a perfect match of the TGS or user principal. As an example, if a middle service tries to replicate the exact S4U2Self communication for exactly the same user, cached referral tickets should be okay. With this enhancement, we increase the use of the Cache and the performance (time, network resources, etc.).
>> 
>> The ReferralsTest is enhanced to reflect these new scenarios and now uses cached S4U2Proxy/S4U2Self referral tickets.
>> 
>> No regressions observed in jdk/sun/security/krb5.
>> 
>> --
>> [1] - https://bugs.openjdk.java.net/browse/JDK-8270137
>
> src/java.security.jgss/share/classes/sun/security/krb5/internal/ReferralsCache.java line 59:
> 
>> 57:         private byte[] clientSvcTicketEnc; // S4U2Proxy only
>> 58:         ReferralCacheKey (PrincipalName cname, PrincipalName sname,
>> 59:                 PrincipalName user, Ticket clientSvcTicket) {
> 
> It's probably not necessary, but I somehow feel it will be clearer to add S4U2Type into the key. In fact, with all these info it almost looks like the key contains everything in a TGS-REQ (except for the timestamp maybe).

Hmm.. in my view, adding the S4U2Type to the key will provide not much value other than minor consistency checks (in the form of debug-mode assertions) because the assumptions that a key with a non-null 'user' value is of S4U2Self type and that a key with a non-null 'clientSvcTicketEnc' value is of S4U2Proxy type (as suggested next to the field decl) are safe. The key type will not be necessary to make a key unique. One more comment to clarify just in case. The clientSvcTicketEnc value is somehow related to the other values in the key but it's not a 1 to 1 field mapping. This is because the TGS is the one that the user-to-be-impersonated sent to the middle service; whilst the cname and sname are related to a middle service ticket. If I'm correct, the cname in the key should match the client service ticket sname (both of them being the middle service name).

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PR: https://git.openjdk.java.net/jdk/pull/5036


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