Re: Security vulnerability in TCP of linux, patches available, how soon in Fedora?

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On 10 August 2016 at 06:44, Rick Walker <walker@xxxxxxxxxxxxxx> wrote:
>
>> 1. Open /etc/sysctl.conf, append a command
>> "/net.ipv4/tcp_challenge_ack_limit = 999999999".
>
> I'm very skeptical.  The default on my stock machine is 100.  You can check
> your own with:
>
>       sysctl -A | grep tcp | grep limit
>
> In the absence of better documentation, I'm guessing that opening the
> ack limit to several million is essentially setting your machine up to
> unlimited hack attack.
>

"   An implementation SHOULD include an ACK throttling mechanism to be
   conservative.  While we have not encountered a case where the lack of
   ACK throttling can be exploited, as a fail-safe mechanism we
   recommend its use.  An implementation may take an excessive number of
   invocations of the throttling mechanism as an indication that network
   conditions are unusual or hostile."
https://tools.ietf.org/html/rfc5961
I'm not an expert on this, but it appears that RFC5961 describes the
mitigation of this type of attack and the ACK rate limiting is simply
a SHOULD for conservation of resources.

-- 
imalone
http://ibmalone.blogspot.co.uk
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