oss-sec mailing list archives
Re: Insecure DNS dependency in many Kerberos deployments
From: Daniel Kahn Gillmor <dkg () fifthhorseman net>
Date: Wed, 16 Aug 2017 18:08:53 -0400
On Wed 2017-08-16 10:52:54 -0700, Russ Allbery wrote:
Florian Weimer <fweimer () redhat com> writes:As a rule of thumb, the impact is similar to running TLS with CA-based certificate validation, but without host name checks (but perhaps slightly less because the trust domains could be much smaller).I think this overstates the impact somewhat. This is more worrisome with TLS because for most TLS applications there is a single global trust domain with certificates issued by dozens or hundreds of parties and no organizational scoping.
fwiw, I think that's what Florian means by his parenthetical aside.
This is a much higher bar to meet, and in a lot of organizations this bar cannot be easily met by an attacker.
While i understand the desire to be clear about the constrained scope of the risk, i think another way of saying what you're saying is "control over one service in a domain and the ability to poison the DNS allows that service operator to masquerade as any other service in the domain". Even for domains where a single administrator controls all machines, this violates principles of privilege separation that admins rely on to be able to deploy potentially-buggy services without putting the other services at risk. So i think it's worth taking this seriously, despite(?) its age and widespread deployment.
For the record, those are settings for *a* Kerberos client library, not *the* Kerberos client library (specifically, the MIT Kerberos implementation). Heimdal does not use those settings, and there are other Kerberos implementations as well.
The fact that some client libraries *don't* do this should give us hope that it's fixable, even in existing deployments :) --dkg
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Current thread:
- Insecure DNS dependency in many Kerberos deployments Florian Weimer (Aug 16)
- Re: Insecure DNS dependency in many Kerberos deployments Daniel Kahn Gillmor (Aug 16)
- Re: Insecure DNS dependency in many Kerberos deployments Russ Allbery (Aug 16)
- Re: Insecure DNS dependency in many Kerberos deployments Daniel Kahn Gillmor (Aug 16)
- Re: Insecure DNS dependency in many Kerberos deployments Russ Allbery (Aug 17)
- Re: Insecure DNS dependency in many Kerberos deployments Daniel Kahn Gillmor (Aug 16)