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Beginning right now, you’ll be able to configure your DNS Firewall to routinely belief all domains in a decision chain (resembling aCNAME, DNAME, or Alias chain).
Let’s stroll via this in nontechnical phrases for these unfamiliar with DNS.
Why use DNS Firewall?
DNS Firewall supplies safety for outbound DNS requests out of your personal community within the cloud (Amazon Virtual Private Cloud (Amazon VPC)). These requests route via Amazon Route 53 Resolver for area title decision. Firewall directors can configure guidelines to filter and regulate the outbound DNS visitors.
DNS Firewall helps to guard towards a number of safety dangers.
Let’s think about a malicious actor managed to put in and run some code in your Amazon Elastic Compute Cloud (Amazon EC2) situations or containers operating inside one in all your digital personal clouds (VPCs). The malicious code is prone to provoke outgoing community connections. It’d achieve this to connect with a command server and obtain instructions to execute in your machine. Or it’d provoke connections to a third-party service in a coordinated distributed denial of service (DDoS) assault. It may additionally attempt to exfiltrate information it managed to gather in your community.
Happily, your community and safety teams are appropriately configured. They block all outgoing visitors besides the one to well-known API endpoints utilized by your app. Thus far so good—the malicious code can not dial again residence utilizing common TCP or UDP connections.
However what about DNS visitors? The malicious code could ship DNS requests to an authoritative DNS server they management to both ship management instructions or encoded information, and it could possibly obtain information again within the response. I’ve illustrated the method within the following diagram.
To stop these eventualities, you need to use a DNS Firewall to watch and management the domains that your functions can question. You may deny entry to the domains that you already know to be dangerous and permit all different queries to cross via. Alternately, you’ll be able to deny entry to all domains besides these you explicitly belief.
What’s the problem with CNAME, DNAME, and Alias information?
Think about you configured your DNS Firewall to permit DNS queries solely to particular well-known domains and blocked all others. Your software communicates with alexa.amazon.com; subsequently, you created a rule permitting DNS visitors to resolve that hostname.
Nevertheless, the DNS system has a number of sorts of information. Those of curiosity on this article are
Ainformation that map a DNS title to an IP handle,CNAMEinformation which can be synonyms for different DNS names,DNAMEinformation that present redirection from part of the DNS title tree to a different a part of the DNS title tree, andAliasinformation that present a Route 53 particular extension to DNS performance. Alias information allow you to route visitors to chose AWS sources, resembling Amazon CloudFront distributions and Amazon S3 buckets
When querying alexa.amazon.com, I see it’s truly a CNAME document that factors to pitangui.amazon.com, which is one other CNAME document that factors to tp.5fd53c725-frontier.amazon.com, which, in flip, is a CNAME to d1wg1w6p5q8555.cloudfront.internet. Solely the final title (d1wg1w6p5q8555.cloudfront.internet) has an A document related to an IP handle 3.162.42.28. The IP handle is prone to be completely different for you. It factors to the closest Amazon CloudFront edge location, probably the one from Paris (CDG52) for me.
An identical redirection mechanism occurs when resolving DNAME or Alias information.
To permit the entire decision of such a CNAME chain, you might be tempted to configure your DNS Firewall rule to permit all names below amazon.com (*.amazon.com), however that might fail to resolve the final CNAME that goes to cloudfront.internet.
Worst, the DNS CNAME chain is managed by the service your software connects to. The chain would possibly change at any time, forcing you to manually preserve the listing of guidelines and approved domains inside your DNS Firewall guidelines.
Introducing DNS Firewall redirection chain authorization
Based mostly on this rationalization, you’re now geared up to grasp the brand new functionality we launch right now. We added a parameter to the UpdateFirewallRule API (additionally accessible on the AWS Command Line Interface (AWS CLI) and AWS Management Console) to configure the DNS Firewall in order that it follows and routinely trusts all of the domains in a CNAME, DNAME, or Alias chain.
This parameter permits firewall directors to solely permit the area your functions question. The firewall will routinely belief all intermediate domains within the chain till it reaches the A document with the IP handle.
Let’s see it in motion
I begin with a DNS Firewall already configured with a domain list, a rule group, and a rule that ALLOW queries for the area alexa.amazon.com. The rule group is hooked up to a VPC the place I’ve an EC2 occasion began.
Once I connect with that EC2 occasion and difficulty a DNS question to resolve alexa.amazon.com, it solely returns the primary title within the area chain (pitangui.amazon.com) and stops there. That is anticipated as a result of pitangui.amazon.com will not be approved to be resolved.
To unravel this, I replace the firewall rule to belief all the redirection chain. I take advantage of the AWS CLI to name the update-firewall-rule API with a brand new parameter firewall-domain-redirection-action set to TRUST_REDIRECTION_DOMAIN.
The next diagram illustrates the setup at this stage.
Again to the EC2 occasion, I attempt the DNS question once more. This time, it really works. It resolves all the redirection chain, right down to the IP handle 🎉.
Due to the trusted chain redirection, community directors now have a simple strategy to implement a method to dam all domains and authorize solely recognized domains of their DNS Firewall with out having to care about CNAME, DNAME, or Alias chains.
This functionality is on the market at no extra price in all AWS Areas. Try it out today!
