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

On 2019/5/13 15:49, Michal Kubecek wrote:

On Mon, May 13, 2019 at 09:33:13AM +0800, Weilong Chen wrote:

quoted

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.

quoted

This path is an another way contrast to iptables rules:
iptables -A input -p icmp --icmp-type timestamp-request -j DROP
iptables -A output -p icmp --icmp-type timestamp-reply -j DROP

Default is disabled to improve security.

If we need a sysctl for this (and I'm not convinced we do), I would
prefer preserving current behaviour by default.

Firewall is not applied to all scenarios.

Michal Kubecek

.

thanks.