Date: Tue, 03 Jan 2012 14:10:03 -0700 From: Kurt Seifried <kseifrie@...hat.com> To: oss-security@...ts.openwall.com Subject: Re: speaking of DoS, openssh and dropbear (CVE-2006-1206) On 01/02/2012 04:33 PM, Nico Golde wrote: > Hi, > * Kurt Seifried <kseifrie@...hat.com> [2012-01-02 04:56]: > [...] > >> The rest of the solutions do not lend themselves to this problem or would >> require significant changes to the OpenSSH protocol/client/server which is a >> bad bad idea. >> >> Anything we do to address this issue should be extremely simple and >> conservative, the OpenSSH server and client are very stable and robust >> pieces of code, any modifications to them make me nervous. >> >> I suspect the simplest and more effective solution might be some form of >> progressive timeout for IP's that fail to authenticate (drop the connection >> entry silently and ignore them in favor of real clients). >> >> Long term I'd like to see more work on hash cash type solutions, being able >> to arbitrarily set or have a reactive system that requires increased work on >> the client end to prove they are a legitimate client would help with this >> whole DoS/DDoS class of problem to some degree. > See above, it would be really nice to see if there is a project which already > does that. hashcash.org has implementations in multiple languages (including a bash script), it uses partial SHA-1 collisions, so easy to do for server, not sure if you can increase/decrease workload on the fly incrementally (i.e. require 16, 17, 18 bit partial matches if the server starts getting loaded). > > Kind regards > Nico > -- -- Kurt Seifried / Red Hat Security Response Team
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