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5.7 Ensure that the EC2 Metadata Service only allows IMDSv2

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Information

When enabling the Metadata Service on AWS EC2 instances, users have the option of using either Instance Metadata Service Version 1 (IMDSv1; a request/response method) or Instance Metadata Service Version 2 (IMDSv2; a session-oriented method).

Instance metadata is data about your instance that you can use to configure or manage the running instance. Instance metadata is divided into

categories

, such as host name, events, and security groups.

When enabling the Metadata Service on AWS EC2 instances, users have the option of using either Instance Metadata Service Version 1 (IMDSv1; a request/response method) or Instance Metadata Service Version 2 (IMDSv2; a session-oriented method). With IMDSv2, every request is now protected by session authentication. A session begins and ends a series of requests that software running on an EC2 instance uses to access the locally stored EC2 instance metadata and credentials.

Allowing Version 1 of the service may open EC2 instances to Server-Side Request Forgery (SSRF) attacks, so Amazon recommends utilizing Version 2 for better instance security.

Solution

From Console:

 - Sign in to the AWS Management Console and navigate to the EC2 dashboard at

https://console.aws.amazon.com/ec2/

.
 - In the left navigation panel, under the INSTANCES section, choose Instances
 - Select the EC2 instance that you want to examine.
 - Choose Actions > Instance Settings > Modify instance metadata options
 - Set Instance metadata service to Enable
 - Set IMDSv2 to Required
 - Repeat steps 1-6 to perform the remediation process for other EC2 instances in all applicable AWS region(s).

From Command Line:

 -

Run the describe-instances command, applying the appropriate filters to list the IDs of all existing EC2 instances currently available in the selected region:

aws ec2 describe-instances --region <region-name> --output table --query "Reservations[*].Instances[*].InstanceId"
 -

The command output should return a table with the requested instance IDs.

 -

Run the modify-instance-metadata-options command with an instance ID obtained from the previous step to update the Instance Metadata Version:

aws ec2 modify-instance-metadata-options --instance-id <instance-id> --http-tokens required --region <region-name>
 -

Repeat steps 1-3 to perform the remediation process for other EC2 instances in the same AWS region.

 -

Change the region by updating --region and repeat the process for other regions.

See Also

https://workbench.cisecurity.org/benchmarks/19631

Item Details

References: CSCv7|5.2

Plugin: amazon_aws

Control ID: 3bad8584a1375f53f62a0a072d58719759397428c71d733e720bceb0ea216481