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Attacks/Breaches

1/30/2019
11:30 AM

Access Control Lists: 6 Key Principles to Keep in Mind

Build them carefully and maintain them rigorously, and ACLs will remain a productive piece of your security infrastructure for generations of hardware to come.
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ACLs Everywhere
Think of the network interface that you'd like to use as the portal for inviting criminal hackers to steal your company IP and your customer PII. Good - that's the interface that you don't want to protect with an ACL
In virtually every piece of security or routing gear, ACLs are applied individually on each interface. That makes complete sense, because you don't want to have the same rules for outward-facing interfaces and those that make up your campus network. But the differences between interfaces are not so great that you want some protected by ACLs and some left bare.
This practice of an ACL on every interface is critical for inbound ACLs - those rules that govern which addresses can send data into your network. Those are the rules that make the biggest, most immediate, difference. With that in mind, though, it's important to remember that ACLs go both ways.
(Image: Chris Titze Imaging - stock.adobe.com)

ACLs Everywhere

Think of the network interface that you'd like to use as the portal for inviting criminal hackers to steal your company IP and your customer PII. Good that's the interface that you don't want to protect with an ACL

In virtually every piece of security or routing gear, ACLs are applied individually on each interface. That makes complete sense, because you don't want to have the same rules for outward-facing interfaces and those that make up your campus network. But the differences between interfaces are not so great that you want some protected by ACLs and some left bare.

This practice of an ACL on every interface is critical for inbound ACLs those rules that govern which addresses can send data into your network. Those are the rules that make the biggest, most immediate, difference. With that in mind, though, it's important to remember that ACLs go both ways.

(Image: Chris Titze Imaging stock.adobe.com)

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paul.dittrich
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paul.dittrich,
User Rank: Strategist
1/30/2019 | 3:40:31 PM
Harnessing the power of ACLs
I could not agree more strongly with every point in your column.

It may be fashionable to claim there is no longer a network perimeter but I still strongly favor using the border router as a "garbage filter".

The BOGONs list? - Drop them all.  Invalid TCP flag combinations - Drop.  No Telnet in your environment?  No FTP?  No RDP?  - Block them all at the border router.

As mentioned in the post, the NGFW should take care of the deep packet inspection for only the traffic you potentially want inside your network.  That firewall should see very little traffic except for the known IPs, ports and protocols which are candidates to be allowed all the way in.

And an outbound ACL (a.k.a. egress filtering) is a very powerful weapon against data exfiltration and many types of malware.  You may still have a Trojan but if it can't phone home......
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