Kaminsky DNS Bug Claimed Fixed By 1-Character Patch

An anonymous reader writes "According to a thread on the bind-users mailing list, there is nothing inherent in the DNS protocol that would cause the massive vulnerability discussed at length here and elsewhere. As it turns out, it appears to be a simple off-by-one error in BIND, which favors new NS records over cached ones (even if the cached TTL is not yet expired). The patch changes this in favor of still-valid cached records, removing the attacker's ability to successfully poison the cache outside the small window of opportunity afforded by an expiring TTL, which is the way things used to be before the Kaminsky debacle. Source port randomization is nice, but removing the root cause of the attack's effectiveness is better."
Update: 08/29 20:11 GMT by KD : Dan Kaminsky sent this note: "What Gabriel suggests is interesting and was considered, but a) doesn't work and b) creates fatal reliability issues. I've responded in a post here."

Comments

Re:OSS wins again

[somersault]

This has more to do with an oversight in the DNS standard - doesn't have anything to do with any single implementation. Windows, Linux, and any other networked system that uses DNS are equally affected.

Besides, it doesn't matter if your operating system is Open Source. You can write closed or open source software on any platform you want, and just because the source is available does not necessarily mean that bugs will be noticed and fixed. This situation just shows that even if there are no 'bugs' in an implementation of a standard, the original design may still be flawed.

I haven't been following this situation very closely, so perhaps I'm a bit off with the details, but I'd be happy for someone to put me right if that's the case.

Favouring cached DNS records seems to me to not be a spectacular idea for all situations. It depends on the length of the TTL setting on your DNS server though. I'm not sure what expiry time would be sensible for an ISP to use. You have to balance the fact that you want to up to date records with the amount of overhead that will be generated by all the DNS traffic.