Cease the CNAME chain battle: Simplified administration with Route 53 Resolver DNS Firewall
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Up to date 2 Could 2024: I eliminated the reference to Route53 Alias that was incorrectly referred as a series
Beginning as we speak, you may configure your DNS Firewall to robotically belief all domains in a decision chain (reminiscent of aCNAMEor DNAMEchain).
Let’s stroll by way of this in nontechnical phrases for these unfamiliar with DNS.
Why use DNS Firewall?
DNS Firewall gives safety for outbound DNS requests out of your personal community within the cloud (Amazon Digital Non-public Cloud (Amazon VPC)). These requests route by way of 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 in opposition to 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 among your digital personal clouds (VPCs). The malicious code is prone to provoke outgoing community connections. It’d accomplish that to connect with a command server and obtain instructions to execute in your machine. Or it would provoke connections to a third-party service in a coordinated distributed denial of service (DDoS) assault. It may also attempt to exfiltrate knowledge it managed to gather in your community.
Luckily, your community and safety teams are accurately configured. They block all outgoing visitors besides the one to well-known API endpoints utilized by your app. To date so good—the malicious code can not dial again house 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 knowledge, and it could possibly obtain knowledge 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 observe and management the domains that your purposes can question. You may deny entry to the domains that to be unhealthy and permit all different queries to go by way of. Alternately, you may deny entry to all domains besides these you explicitly belief.
What’s the problem with CNAME and DNAME data?
Think about you configured your DNS Firewall to permit DNS queries solely to particular well-known domains and blocked all others. Your utility 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 kinds of data. Those of curiosity on this article are
Adata that map a DNS title to an IP handle,CNAMEdata which can be synonyms for different DNS names,DNAMEdata that present redirection from part of the DNS title tree to a different a part of the DNS title tree, and
When querying alexa.amazon.com, I see it’s truly a CNAME report that factors to pitangui.amazon.com, which is one other CNAME report 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 report related to an IP handle 3.162.42.28. The IP handle is prone to be totally different for you. It factors to the closest Amazon CloudFront edge location, doubtless the one from Paris (CDG52) for me.
An analogous redirection mechanism occurs when resolving DNAME data.
To permit the whole decision of such a CNAME chain, you can be tempted to configure your DNS Firewall rule to permit all names underneath amazon.com (*.amazon.com), however that may fail to resolve the final CNAME that goes to cloudfront.internet.
Worst, the DNS CNAME chain is managed by the service your utility 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
Primarily based on this rationalization, you’re now geared up to know the brand new functionality we launch as we speak. We added a parameter to the UpdateFirewallRule API (additionally obtainable on the AWS Command Line Interface (AWS CLI) and AWS Administration Console) to configure the DNS Firewall in order that it follows and robotically trusts all of the domains in a CNAMEor DNAMEchain.
This parameter permits firewall directors to solely permit the area your purposes question. The firewall will robotically belief all intermediate domains within the chain till it reaches the A report with the IP handle.
Let’s see it in motion
I begin with a DNS Firewall already configured with a area listing, a rule group, and a rule that ALLOW queries for the area alexa.amazon.com. The rule group is connected to a VPC the place I’ve an EC2 occasion began.
Once I connect with that EC2 occasion and challenge 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 isn’t approved to be resolved.
To resolve 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 ????.
Because of the trusted chain redirection, community directors now have a simple technique to implement a method to dam all domains and authorize solely identified domains of their DNS Firewall with out having to care about CNAMEor DNAMEchains.
This functionality is out there at no further value in all AWS Areas. Attempt it out as we speak!
