OB1
Premium
join:2006-07-17
ITALY
| reply to swilbourn
Re: [DNS] Comcast and the DNS Server flaw issue
said by swilbourn :
Sorry, but BIND and Nominum don't share any code. Nominum's servers are not derived from BIND at all, and in fact, has a different underlying design.
Yes ok, I was somewhat "smokey" and probably not correct, but my post was directed to Dan, and I hope he understood what I meant 
--
* ObiWan
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swilbourn
@comcast.net
| reply to OB1
A previous poster wrote,
"Uhmmm... maybe not to the vanilla stuff... but since nominum and ISC BIND share some "codebase", I wonder if nominum may be vulnerable to a certain "collision attack""
Sorry, but BIND and Nominum don't share any code. Nominum's servers are not derived from BIND at all, and in fact, has a different underlying design.
Sandy Wilbourn
VP Engineering, Nominum
wilbourn@nominum.com |
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OB1
Premium
join:2006-07-17
ITALY
| reply to Dan Kaminsky
said by Dan Kaminsky :
This is Dan Kaminsky, the original finder of the bug.
LOL... Hi there Dan, this world is really small, isn't it  ?
said by Dan Kaminsky :
ComCast is using Nominum, the company that employs the inventor of DNS. Nominum has some extra protections that slow my attack down by a couple hundred times. (I called BS on Nominum and they were only too happy to give me a server to try to break. I eventually did, but not in 10 seconds like everyone else but DJB/power.)
Uhmmm... maybe not to the vanilla stuff... but since nominum and ISC BIND share some "codebase", I wonder if nominum may be vulnerable to a certain "collision attack" 
Did you try it ? |
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Dan Kaminsky
@speakeasy.net | reply to jbob
The new bug is much worse than the old one -- predictable TXID wouldn't override cache, since there wouldn't be another race. |
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espaeth
Digital Plumber
Premium,MVM
join:2001-04-21
Minneapolis, MN
 ·voip.ms
·Vitelity VOIP
·Callcentric
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·ViaTalk
 ·Comcast
 ·Embarq
| reply to Alan Clegg
Re: Transaction ID is just not enough (even if 100% "random")
said by Alan Clegg :
If you have sufficient transaction ID randomness, then to a certain degree the source port randomness is just an academic bonus.
You sir, are completely incorrect. Completely ?
I will acknowledge that I overstated on source port randomness just being a bonus. Still, the most exploitable servers are those that are still using fixed source port queries, followed by the previous bind implementations that still had limited entropy for both the source port and transaction ID.
The servers being reported with "poor" source port randomness (ie, randomness within a fixed range) but "good" for transaction ID randomness are still better off than those servers out there still susceptible to »securitytracker.com/alerts/2007/···442.html . |
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Alan Clegg
@rr.com
 from:
Cabal 
| reply to espaeth
If you have sufficient transaction ID randomness, then to a certain degree the source port randomness is just an academic bonus.
The issue with Bind was that both the source port and the transaction ID for the requests were predictable, which made the poisoning not just possible, but actually quite likely if you scripted things correctly.
You sir, are completely incorrect.
Alan Clegg
aclegg@isc.org |
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CableUZR
Cuidado, Hay Llamas
join:2003-02-04
Mount Holly, NJ
clubs:
| reply to jbob
Re: just copy/pastin' my way through life
To me it looks as though the test performed by OARC is using too small a sample size to give accurate standard of deviation numbers (the results seem precise, just not accurate). Standard deviation seems to be the only difference between results on the servers tested, and the difference is quite slight. As mentioned, the fact that some randomness has been added to the mix is a good thing, and makes exploiting the flaw much less likely. Could it be better? -Sure. Is it better than not patching at all -you bet. What would be a sufficient sample size to judge the randomness of the DNS resolver? -Ask a statistician...
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[/home/USA]$rm -rf /bin/bible_beaters |
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jbob
Reach Out and Touch Someone
Premium
join:2004-04-26
Little Rock, AR
·Comcast
·AT&T Southwest
1 edit | reply to Dan Kaminsky
Re: [DNS] Comcast and the DNS Server flaw issue
Hi Dan Thanks for stopping by and welcome to DSLR.
So I take what you're saying is Comcast has been doing a good job and probably that using their DNS servers is perhaps ok!
After reading what Eric espaeth wrote about the dns-oarc test I suppose it's more geared toward BIND and may not be as accurate testing the Comcast DNS nameservers?
Still it's disconcerting for us non network engineer types to see one test pass and another show issues. 
Glad you could join in. |
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espaeth
Digital Plumber
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join:2001-04-21
Minneapolis, MN
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| reply to rolfp
Re: just copy/pastin' my way through life
said by rolfp :OK, however, the folks at the thread in ATU I link are reporting 'GOOD' results when they apply the patch or update their dns server software. Wouldn't such a 'GOOD' result be expected from a patched Comcast server It would depend on what DNS server it is. These tools are for testing Bind, so they are assuming Bind post-patch behavior. The 3 key problems with Bind specifically are:
1) Transaction IDs were predictable
2) Source ports were predictable
3) There was no limit to the number of response "attempts" that would be processed for a query before a valid response is received.
For this exploit to work, you need to get a spoofed response packet shot into the DNS server before the real server's packet made it in. With bind you could predict what the next source port and transaction ID would be, so once you saw one query you could predict what the next would be. |
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Dan Kaminsky
@speakeasy.net | reply to jbob
Re: [DNS] Comcast and the DNS Server flaw issue
This being said, whatever ports you see, are the ports I'm seeing. I don't have time to fake records |
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Dan Kaminsky
@speakeasy.net
| reply to jbob
This is Dan Kaminsky, the original finder of the bug.
ComCast is using Nominum, the company that employs the inventor of DNS. Nominum has some extra protections that slow my attack down by a couple hundred times. (I called BS on Nominum and they were only too happy to give me a server to try to break. I eventually did, but not in 10 seconds like everyone else but DJB/power.)
A couple hundred times harder to attack corresponds to ~8 bits of entropy, which is how short they are right now. They're investigating now if they can get a couple of bits more in, just for added security. But I do think Nominum, and ComCast by extension, need some credit for working to develop more intensive protections against this attack -- even if it's much less convenient for those of us building test tools.
I am a little amused at the comments re: strong arming. It's not every day that Comcast and I are on the same side of the fence (ahem, net neutrality). This is however a much graver threat, and frankly more ISP's need to follow Comcast's lead here (now there are words I never thought I'd write!). |
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deblin
Dark Side of the Moon
Premium,MVM
join:2001-09-01
Middletown, DE
| reply to rolfp
Re: just copy/pastin' my way through life
Verizon still has not addressed the issue for the source port randomness on their DNS servers either:
»7079aa1c5d30a1b7ccc245e6.et.dns-oarc.net/
I'm considering removing the forwarders I use for my caching nameserver, until Verizon gets their act together.
--
perl -le 'print $i=pack(c5,(8**2+3**2),42-10,sqrt(3600),oct(63),(unpack(c, "&")-6)),pack(c7, (70,114,101,101,66,83,68))' |
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rolfp
join:2001-09-12
Oakland, CA | reply to espaeth
OK, however, the folks at the thread in ATU I link are reporting 'GOOD' results when they apply the patch or update their dns server software. Wouldn't such a 'GOOD' result be expected from a patched Comcast server? |
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espaeth
Digital Plumber
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Minneapolis, MN
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| reply to rolfp
If you have sufficient transaction ID randomness, then to a certain degree the source port randomness is just an academic bonus.
The issue with Bind was that both the source port and the transaction ID for the requests were predictable, which made the poisoning not just possible, but actually quite likely if you scripted things correctly. |
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jbob
Reach Out and Touch Someone
Premium
join:2004-04-26
Little Rock, AR
·Comcast
·AT&T Southwest
2 edits | reply to rolfp
Here's the results of the same test. Dang results all over the place:
»550534c6b13985d060430715.et.dns-oarc.net/
Oh and this is with Comcasts's DNS nameservers
Same test using OpenDNS nameservers.
»9656593288a74b47aa1c9010.et.dns-oarc.net/
Much better
So what are us lowly non network engineer types supposed to make of this. Is this a flawed test of Comcast or is the DoxPara test more accurate? |
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rolfp
join:2001-09-12
Oakland, CA
·Comcast
·EarthLink
| reply to Sandy Wilbourn
afaict, this issue is being discussed, also, at ATU, with another diagnostic test for the vulnerability:
»CERT VU#800113 DNS Cache Poisoning Issue
This is not my bailiwick but that test seems not to give positive results for me.
dns-oarc has a web-test, also: »https://www.dns-oarc.net/
[..] |
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Sandy Wilbourn
@nominum.com
| reply to Comcast_DNS
Re: [DNS] Comcast and the DNS Server flaw issue
I'm not sure that I understand this post.
I have worked closely with Comcast on this whole thing since May (I am not a Comcast employee). They have been one of the most concered ISPs since that time. Comcast was very proactive and patched their DNS servers before the CERT advisory. That's a hugely positive thing and took moving a lot of parts around to get it done.
Then web-based tests to approximate the exploit were developed and released by multiple security analysts. BUT, if web-based tests do not accurately reflect a vulnerability that they expressly test for, do you not think they should be updated for accuracy? What you see is not those analysts being pressured by anyone. If you doubt that, you should contact Dan and others and ask them. Our interest should be in people having tests that accurately reflect whether or not a DNS is patched.
Sandy |
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jbob
Reach Out and Touch Someone
Premium
join:2004-04-26
Little Rock, AR
·Comcast
·AT&T Southwest
| reply to Sandy Wilbourn
said by Sandy Wilbourn :
It's been a great service to see these various testers on the Internet. However, different folks have used different implementations at different times and have gotten inconsistent results.
Dan's test is the best one out there, but even Dan has gone through a couple of iterations as we all try to warn people about this DNS vuln.
1. On July 8th, it reported that Comcast servers were protected.
2. A few days later, Dan became concerned with some issues having to do with firewalls and NATs. He changed the test so that Comcast servers received the results from the first message above.
3. Tuesday, he changed his test again to account for the capabilities in the Comcast servers.
I tried the tool tonight on my home Comcast connection, and it showed Comcast's servers as being protected!
Sandy Wilbourn
VP Engineering, Nominum
Good info Sandy
Hopefully I made it clear in my Topic post that may or may be an issue as things seem to be changing which is exactly what we have seen. I wonder however if Dan will change his test again? lol
Looks like it might be ok to go back to Comcast DNS servers. I just wanted Comcast users to be informed of any possible issues. |
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Comcast_DNS
@aol.com
thumbs down from:
Cabal
| reply to jlivingood
said by jlivingood :That may also reflect an evolution of the tests themselves. Wow, the Comcast culture is simply amazing.
First Dan Kaminsky faked the port range used by the Comcast DNS (and only the Comcast DNS), but after pressure from Comcast, he stopped doing it. Of course this is what happened, how could anyone think otherwise. |
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jlivingood
Premium,VIP
join:2007-10-28
Philadelphia, PA
| reply to Comcast_DNS
said by Comcast_DNS :OK. my previous test display was 24 hours old, so I just repeated it, and the DNS warning is no longer there. However, the port range also seems to have been increased, which indicates to me that perhaps there were changes in the Comcast DNS infrastructure as well as possible changes in Dam Kaminsky's test. If so, then Comcast deserves praise for being so responsive, but instead we get typical Comcast denials, I guess some parts of the Comcast corporate culture are hard to shed.  Your name server, at 68.87.68.164, appears to be safe, but make sure the ports listed below aren't following an obvious pattern.
------------------------------------------
Requests seen for d1df9c73c1f1.toorrr.com:
68.87.68.164:17824 TXID=2180
68.87.68.164:16908 TXID=31062
68.87.68.164:17486 TXID=58678
68.87.68.164:17804 TXID=43870
68.87.68.164:17734 TXID=59408
That may also reflect an evolution of the tests themselves.
JL |
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