AWS Certified Specialty SCS-C03 Updated Exam

The immediate containment step for exposed access keys is todisable (deactivate) the compromised IAM access key(Option B). This prevents any further use of the leaked credentials, which is essential once secrets are publicly exposed. Creating a new key (Option D) may be part of recovery later, but it does not stop abuse of the already exposed key unless the exposed key is first deactivated.

To determine whether the credentials were used, you need evidence of access activity. Among the provided options, the best fit is generating and reviewing theIAM credential report(Option E). The report includes metadata such as access key status and “last used” style details that help triage whether the user’s credentials have been exercised recently. While deeper investigation would typically rely on CloudTrail “AccessKeyId” searches, the credential report is a quick AWS-native step aligned to the answer choices.

Option A is not correct: IAM Access Analyzer helps identify external access paths to resources and validate policies; it does not provide a definitive history of what a specific access key did. Option C is not a GuardDuty capability—GuardDuty generates findings; it does not “block” a specific access key. Therefore, deactivating the key and using credential reporting to assess recent usage best matches the requirements.

Amazon EC2 security groups arestateful, meaning that once a connection is established, return traffic is automatically allowed, even if the inbound rule that originally permitted the connection is later removed. According to the AWS Certified Security – Specialty Official Study Guide and Amazon EC2 security documentation,existing connections are not terminated when security group rules change. This explains why the SSH session remains active even after the security group rules were modified, while new traffic such as ICMP ping is blocked.

To immediately and fully isolate an EC2 instance during an incident response scenario, AWS recommends usingstateless network controls. Amazon VPC network ACLs (NACLs) arestateless, which means that every packet is evaluated against the ACL rules regardless of whether the traffic is part of an existing connection. When a deny rule is added,all traffic is immediately blocked, including active sessions.

By creating a network ACL and associating it with the subnet that contains the target instance, and by adding explicit deny rules with the lowest rule numbers for both inbound and outbound traffic, the security engineer ensures thatall network communication to and from the instance is immediately interrupted. This approach satisfies the requirement to isolate the instance while preserving its runtime state and memory for forensic analysis.

Other options fail to meet the requirement because security group modifications do not terminate existing sessions, Systems Manager does not enforce network isolation, and host-level firewall changes require instance-level access and do not provide immediate, network-enforced isolation.

AWS Certified Security – Specialty Official Study Guide

Amazon EC2 Security Groups Documentation

Amazon VPC Network ACL Documentation

AWS Incident Response Best Practices

In a properly segmented VPC architecture,public subnets route internet-bound traffic to an internet gateway, whileprivate subnets route outbound internet traffic through a NAT gatewaythat resides in a public subnet. According to the AWS Certified Security – Specialty Official Study Guide and Amazon VPC documentation, private subnets must never have a direct route to an internet gateway.

The issue described indicates that private subnets are incorrectly routing traffic directly to the internet gateway. To remediate this, aNAT gateway must be provisioned in each public subnetto ensure high availability across Availability Zones. This satisfies the requirement that private resources can initiate outbound connections without being directly reachable from the internet.

Next, the route tables associated with theprivate subnets must be updatedso that the default route (0.0.0.0/0) points to the NAT gateway in the same Availability Zone. This ensures proper traffic flow and prevents cross-AZ dependencies.

Option B is incorrect because NAT gateways must reside in public subnets. Option C is unnecessary because local routes to the VPC CIDR range are automatically created. Option E is explicitly insecure, as it would reintroduce direct internet gateway access from private subnets.

AWS documentation consistently identifiesNAT gateways plus correct private subnet routingas the standard design for secure VPC segmentation.

AWS Certified Security – Specialty Official Study Guide

Amazon VPC Route Table Documentation

AWS Well-Architected Framework – Security Pillar

Before beginning an investigation, incident response best practice is topreserve evidence,prevent accidental loss of the asset, andclearly mark and control the potentially affected resource. Enablingtermination protection(Option B) helps ensure the instance is not accidentally terminated during triage, which would destroy volatile evidence and complicate forensics and recovery.

TakingEBS snapshotsof all attached data volumes (Option C) preserves a point-in-time copy of disk evidence for later forensic analysis, malware scanning, or offline investigation. Snapshots allow responders to create forensic volumes or AMIs in an isolated environment without repeatedly touching the potentially compromised instance.

Capturinginstance metadataand tagging the instance asunder quarantine(Option E) supports both investigation and operational control. Metadata capture (instance ID, IAM role, network interfaces, security groups, user-data, tags, recent changes) provides context for responders. Quarantine tagging enables automated workflows (for example, incident runbooks that isolate the instance, restrict IAM, or move it to a quarantine security group) and signals to other teams/tools that the instance is under investigation.

Option A is the opposite of what you want. Option D destroys evidence. Option F is not an appropriate “before investigation” step; altering metadata risks losing evidence and is not the primary containment approach.