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Beginning as we speak, you possibly can configure your DNS Firewall to mechanically belief all domains in a decision chain (akin to aCNAME, DNAME, or Alias chain).
Let’s stroll by this in nontechnical phrases for these unfamiliar with DNS.
Why use DNS Firewall?
DNS Firewall offers safety for outbound DNS requests out of your personal community within the cloud (Amazon Digital Non-public Cloud (Amazon VPC)). These requests route by Amazon Route 53 Resolver for area title decision. Firewall directors can configure guidelines to filter and regulate the outbound DNS site 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 working inside considered one of your digital personal clouds (VPCs). The malicious code is prone to provoke outgoing community connections. It would accomplish that to hook up 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 information it managed to gather in your community.
Happily, your community and safety teams are accurately configured. They block all outgoing site visitors besides the one to well-known API endpoints utilized by your app. To this point so good—the malicious code can’t dial again house utilizing common TCP or UDP connections.
However what about DNS site 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 will possibly obtain information again within the response. I’ve illustrated the method within the following diagram.
To stop these situations, you should utilize a DNS Firewall to observe and management the domains that your purposes can question. You possibly can deny entry to the domains that you already know to be unhealthy and permit all different queries to go by. Alternately, you possibly can deny entry to all domains besides these you explicitly belief.
What’s the problem with CNAME, DNAME, and Alias data?
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 site visitors to resolve that hostname.
Nevertheless, the DNS system has a number of forms of data. Those of curiosity on this article are
Adata that map a DNS title to an IP deal with,CNAMEdata which might 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, andAliasdata that present a Route 53 particular extension to DNS performance. Alias data allow you to route site visitors to chose AWS sources, akin to Amazon CloudFront distributions and Amazon S3 buckets
When querying alexa.amazon.com, I see it’s really 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.web. Solely the final title (d1wg1w6p5q8555.cloudfront.web) has an A report related to an IP deal with 3.162.42.28. The IP deal with is prone to be totally different for you. It factors to the closest Amazon CloudFront edge location, seemingly the one from Paris (CDG52) for me.
An identical redirection mechanism occurs when resolving DNAME or Alias data.
To permit the whole decision of such a CNAME chain, you may be tempted to configure your DNS Firewall rule to permit all names beneath amazon.com (*.amazon.com), however that may fail to resolve the final CNAME that goes to cloudfront.web.
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 keep the record of guidelines and licensed 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 out there on the AWS Command Line Interface (AWS CLI) and AWS Administration Console) to configure the DNS Firewall in order that it follows and mechanically trusts all of the domains in a CNAME, DNAME, or Alias chain.
This parameter permits firewall directors to solely permit the area your purposes question. The firewall will mechanically belief all intermediate domains within the chain till it reaches the A report with the IP deal with.
Let’s see it in motion
I begin with a DNS Firewall already configured with a area record, 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.
After I connect with that EC2 occasion and situation 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 licensed to be resolved.
To resolve this, I replace the firewall rule to belief the whole 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 strive the DNS question once more. This time, it really works. It resolves the whole redirection chain, all the way down to the IP deal with 🎉.
Due to the trusted chain redirection, community directors now have a simple technique 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 further price in all AWS Areas. Attempt it out as we speak!