≡ Menu

The design of Windows 10 allows the Operating System to send DNS queries to all the available interfaces on the machine. The OS does not take into account the network interface priority nor does it take into account any default route.

This design is somewhat okay until we face a VPN scenario where the DNS request has to go through the VPN tunnel for security reasons and this will allow a hacker to intercept a DNS request and modify the reply to perform a man-in-the-middle attack.

The easy fix it to add a DWORD name of DisableSmartNameResolution with a value of 0 under the following path.

HKEY_LOCAL_MACHINE\Software\Policies\Microsoft\Windows NT\DNSClient

RFC 3330 Traffic Filtering From The Internet

The following post will explain one of the recommended method of filtering unwanted traffic from the internet to the internal network.

Most administrators filter RFC-1918 traversing from the internet to internal networks, while they are allowing a list of bogons prefixes which is defined in RFC-3330. These addresses are _not_ publically assigned, therefore should not see them as source IP destined to your internal network. Furthermore, it is a best practice from a security prospective to filter these ranges in case you are targeted with a spoofing attack.

As a reference to this post, please check RFC-3330 which contains all the prefixes in question.
[click to continue…]

How to Configure Failover on Cisco ASA Firewall

Configuring a Cisco ASA firewall to achieve resiliency is straightforward. Implementing the failover feature in the firewall to be on Active Standby mode can achieved by the following commands.

Please note that it is not recommended to use the Management interface for failover purposes, especially for stateful failover in which the security appliance constantly sends the connection information from one security appliance to the other.

Furthermore, we have to consider the future implication of using such Management Interface, as you may be want to create a completely new network for the Out Of Bound (OOB) access where the Management Interface on each device will participate. Therefore, using a Management Interface might cause design issues in the future.

On this example below, I will be using GigabitEthernet0/5 on both devices as the Failover interface.
[click to continue…]

How to Configure Firewall on Linux

Below I will go over three easy steps on Configuring IPTables Firewall on Linux Environment. The following configuration was tested on 64 Bit Debian.

The firewall itself consists of two configuration files located in the following location.

/etc/default/firewall-rules consist the firewalls rules which are editable by the user.
/etc/init.d/firewall is the script for start|stop|restart|status of the firewall.

Below you can see Sample Firewall Rules. This script resides in /etc/default/firewall-rules

Please use this as a template and replace the EXIF, EXTIP and other IP Address / Ranges.

[click to continue…]

DNSSec Effect on ASA / PIX Firewalls & FWSMs

As of 5th May 2010 All 13 DNS ROOT Server will consist of a signed digital signature with every replied query. This has been ruled out to tackle any man-in-middle attack similar to Dan Kaminsky’s exploit.

Is it going to break the internet?

It is only going to affect if the firewalls & FWSM are not configured correctly to allow DNSSEC signed packets.

The answer being, as we already know DNS uses UDP packets for query replies; and most firewalls are going to drop any packets larger than 512bytes.

Having been said, the DNSSEC signed replies are going to have an extra layer of encryption, thus increasing the packet size up to 4KB (4096) and the firewalls & FWSMs needs to be configured to allow such larger packets through.

What needs to be configured on the Firewall?

The firewall needs to have the following settings to allow larger UDP packets through…

message-length maximum 4096

We can either hard-code the maximum-length or use other methods to tackle this issue.

More info about DNSSEC can be found on http://www.root-dnssec.org or simply typing the word on Google.

How to Configure IPSec VPN

I have come across an odd scenario on pre-share key based IPSec tunnels…

The question being, when an IPSec tunnel is active (Phase 1 and 2 are UP) and the pre-share key is changed, does this tear down the tunnel?

The tunnel configuration on R4 follows…

crypto isakmp policy 1
 encr aes 256
 hash md5
 authentication pre-share
 group 2
crypto isakmp key fnode address
crypto ipsec transform-set FNODE1 esp-3des esp-sha-hmac
crypto map FNODE1 1 ipsec-isakmp
 set peer
 set transform-set FNODE1
 match address 120

interface Ethernet0/0
 ip address
 crypto map FNODE1

access-list 120 permit ip

The tunnel configuration on R5 follows…

[click to continue…]

Copyright © Nish Vamadevan 2002-2018. All Rights Reserved. Terms and Policies.