Hash collisions vulnerability in web servers

Published: 2011-12-28
Last Updated: 2011-12-28 23:02:14 UTC
by Daniel Wesemann (Version: 2)
8 comment(s)

A new vulnerability advisory by security firm n-runs [1] describes how hash tables in PHP5,Java,ASP.NET and others can be attacked with deliberate collisions in the hash function, leading to a denial of service (DoS) on the web server in question. Microsoft have already responded with an advisory [2] of their own, other vendors are likely to follow.

Updated 2300UTC: MSFT published additional information [3] on how to detect and mitigate an attack.

[1] http://www.nruns.com/_downloads/advisory28122011.pdf
[2] http://technet.microsoft.com/en-us/security/advisory/2659883
[3] http://blogs.technet.com/b/srd/archive/2011/12/27/more-information-about-the-december-2011-asp-net-vulnerability.aspx


8 comment(s)
ISC StormCast for Wednesday, December 28th 2011 http://isc.sans.edu/podcastdetail.html?id=2221

.nl.ai ?

Published: 2011-12-28
Last Updated: 2011-12-28 00:51:54 UTC
by Daniel Wesemann (Version: 1)
0 comment(s)

Now .. where is nl.ai ?? Dot-ai is Anguilla, a speck of land in the Caribbean, to the east of Puerto Rico. And probably has nothing at all to do with what follows. Dot-nl-dot-ai, on the other hand, appears to be a free domain name registrar.

If you're into malware analysis, you've probably seen your fair share of .nl.ai domains recently. And not just these. Feeding "nl.ai" into RUS-CERTs Passive DNS collector http://www.bfk.de/bfk_dnslogger.html?query=ns1.cd.am#result gives us the name server for .nl.ai (one ns1.cd.am), which in turn shows a couple of other domains that are currently very familiar to the malware analyst. Like .c0m.li, and .cc.ai.

If you are blocking domains on your gateway or DNS server, blackholing these few


might be a reasonable move, at least until someone in your business can show that they have a legitimate need to access one of the sub domains of these pseudo top level domains. Mind you, chances are that not all domains hosted there in fact are bad. But all the ones that I've seen in my logs so far: were.



Keywords: malware
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