EC2/UnusualDNSResolve- Guard Duty


Hi Team, I am getting EC2/UnusualDNSResolve for my private windows Ec2 instance. DNS IP: network settings are not changed. can you help me to find the this finding is triggered Regards.

asked 10 months ago2544 views
2 Answers

Hi, see for details

An Amazon EC2 instance is communicating with an unusual public DNS resolver.
Default severity: Medium

Data source: VPC flow logs

This finding informs you that the listed Amazon EC2 instance in your AWS environment
 is behaving in a way that deviates from the baseline behavior. This EC2 instance 
has no recent history of communicating with this public DNS resolver. The Unusual 
field in the finding details panel in the GuardDuty console can provide information 
about the queried DNS resolver.

Remediation recommendations:

If this activity is unexpected, your instance may be compromised. 
For more information, see Remediating a compromised EC2 instance.

So, basically, it says that your instance has started to talk with a new DNS server (it never queried it before). This unusual resolver will be listed on the Gard Duty panel. Check if it's a safe DNS resolver or not. If not, you will have to prevent your instance from talking to it.

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answered 10 months ago
  • Hello, Thanks for the information. But, I need to find why my instance communicating with public Dns resolver ( And unable to predict whether it is safe or unsafe. Note: we have not changed instance's network Dns settings. Also help us how to prevent it.( we are getting this alert for few of our ec2 instances)

    We do have site to site vpn configured for this VPV. any of vpn's dns setting makking this issue?

0 is Google DNS Servers. Nothing to worry about much on the security end unless you have a DNS Server that your instances should be using

answered 10 months ago

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