Skip to main content

domain name system - Protecting my Bind dns server from slow kaminsky-style cache poisoning attacks

Dan Kaminsky described how DNS servers could be poisoned with spoofed DNS responses [1]. As I understand it, the problem was that Kaminsky found a way to account for most other sources of randomness in a DNS query such that the main barrier to an attacker was in guessing the DNS query id (16 bits of entropy) when generating a spoofed response. An attacker could, on average, spoof the response within 32k guesses. So, the recommended mitigation was to randomize the source port, and everyone applied their patches and all was well.




Except that this only brought up the number of guesses from 32k to somewhere between 134m to 4b. Sure, it couldn't be done quickly, but a patient attacker could still do this slowly - in fact, Bert Hubert calculated that an attack at 100qps has 50% chance of success within 6 weeks. [2]



I don't have sufficient reputation to post more links. However, I see that many technical approaches have been considered, such as draft-wijngaards-dnsext-resolver-side-mitigation-01 and draft-vixie-dnsext-dns0x20-00 on tools.ietf.org, RFC5452 as well as the Google Public DNS security docs:




  1. DNS label bit 0x20 (ie, cAsE.gAmEs)




    • does Bind do this? I can't believe that Bind wouldn't implement something that Vixie proposed


    • still, an attack could force the query of domains whose case cannot be significantly munged. eg. "d293823."


  2. RTT banding, IPv4/IPv6 selection, source address randomisation (from wijngaards)




    • I don't think this will add significant entropy, but I'd do it if Bind can.


  3. Authority query for NS/nameserver/A/AAAA after referral (from wijngaards)





    • This seems to be an elegant solution. Don't understand the problems with it. It might not be the preferred solution for large scale deployment, but it seems reasonable for my site. Can Bind do this?


  4. Attack mode trouble counter




    • Can Bind do this?

    • However, if I have a statefull firewall in front of the DNS server, the DNS server's trouble counter will never see spoofed responses arriving with the wrong destination port right?


  5. Fallback to TCP (especially after going into attack mode)


  6. Ask twice/thrice (especially after going into attack mode)



  7. Removing duplicate queries (from Google Public DNS)




Unfortunately, I don't see any configuration options for turning these on even in the latest version of Bind.



So I would like to ask what else can be done to protect against this style of spoofing attacks, specifically when I am running Bind. If the mitigation remains a probabilistic thing, I'd like for the odds to be stacked against the attack succeeding in a million years.



[1] http://s3.amazonaws.com/dmk/DMK_BO2K8.ppt



[2] http://ds9a.nl/har-presentation-bert-hubert-3.pdf slide 24.

Comments

Post a Comment

Popular posts from this blog

linux - iDRAC6 Virtual Media native library cannot be loaded

When attempting to mount Virtual Media on a iDRAC6 IP KVM session I get the following error: I'm using Ubuntu 9.04 and: $ javaws -version Java(TM) Web Start 1.6.0_16 $ uname -a Linux aud22419-linux 2.6.28-15-generic #51-Ubuntu SMP Mon Aug 31 13:39:06 UTC 2009 x86_64 GNU/Linux $ firefox -version Mozilla Firefox 3.0.14, Copyright (c) 1998 - 2009 mozilla.org On Windows + IE it (unsurprisingly) works. I've just gotten off the phone with the Dell tech support and I was told it is known to work on Linux + Firefox, albeit Ubuntu is not supported (by Dell, that is). Has anyone out there managed to mount virtual media in the same scenario?
Post a Comment
Read more

hp proliant - Smart Array P822 with HBA Mode?

We get an HP DL360 G8 with an Smart Array P822 controller. On that controller will come a HP StorageWorks D2700 . Does anybody know, that it is possible to run the Smart Array P822 in HBA mode? I found only information about the P410i, who can run HBA. If this is not supported, what you think about the LSI 9207-8e controller? Will this fit good in that setup? The Hardware we get is used but all original from HP. The StorageWorks has 25 x 900 GB SAS 10K disks. Because the disks are not new I would like to use only 22 for raid6, and the rest for spare (I need to see if the disk count is optimal or not for zfs). It would be nice if I'm not stick to SAS in future. As OS I would like to install debian stretch with zfs 0.71 as file system and software raid. I have see that hp has an page for debian to. I would like to use hba mode because it is recommend, that zfs know at most as possible about the disk, and I'm independent from the raid controller. For us zfs have many benefits,
Post a Comment
Read more

apache 2.2 - Server Potentially Compromised -- c99madshell

So, low and behold, a legacy site we've been hosting for a client had a version of FCKEditor that allowed someone to upload the dreaded c99madshell exploit onto our web host. I'm not a big security buff -- frankly I'm just a dev currently responsible for S/A duties due to a loss of personnel. Accordingly, I'd love any help you server-faulters could provide in assessing the damage from the exploit. To give you a bit of information: The file was uploaded into a directory within the webroot, "/_img/fck_uploads/File/". The Apache user and group are restricted such that they can't log in and don't have permissions outside of the directory from which we serve sites. All the files had 770 permissions (user rwx, group rwx, other none) -- something I wanted to fix but was told to hold off on as it wasn't "high priority" (hopefully this changes that). So it seems the hackers could've easily executed the script. Now I wasn't able
Post a Comment
Read more