netdev - Re: [PATCH net-next] ipv4: Add support to disable icmp timestamp

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Date:   Mon, 13 May 2019 13:49:00 +0200
From:   Michal Kubecek <mkubecek@...e.cz>
To:     netdev@...r.kernel.org
Cc:     Weilong Chen <chenweilong@...wei.com>, davem@...emloft.net,
        kuznet@....inr.ac.ru, yoshfuji@...ux-ipv6.org
Subject: Re: [PATCH net-next] ipv4: Add support to disable icmp timestamp

On Mon, May 13, 2019 at 07:38:37PM +0800, Weilong Chen wrote:
> 
> On 2019/5/13 15:49, Michal Kubecek wrote:
> > On Mon, May 13, 2019 at 09:33:13AM +0800, Weilong Chen wrote:
> > > The remote host answers to an ICMP timestamp request.
> > > This allows an attacker to know the time and date on your host.
> > 
> > Why is that a problem? If it is, does it also mean that it is a security
> > problem to have your time in sync (because then the attacker doesn't
> > even need ICMP timestamps to know the time and date on your host)?
> > 
> It's a low risk vulnerability(CVE-1999-0524). TCP has
> net.ipv4.tcp_timestamps = 0 to disable it.

That does not really answer my question. Even if "CVE" meant much more
back in 1999 than it does these days, none of the CVE-1999-0524
descriptions I found cares to explain why it's considered a problem that
an attacker knows time on your machine. They just claim it is. If we
assume it is a security problem, then we would have to consider having
correct time a security problem which is something I certainly don't
agree with.

One idea is that there may be applications using current time as a seed
for random number generator - but then such application is the real
problem, not having correct time.

Michal Kubecek