SCS-C03 Exam Dumps - AWS Certified Security – Specialty

A rate-based rule in AWS WAF is designed to quickly mitigate spikes and potential layer 7 floods bytracking request rates per originating IPand temporarily blocking (or counting/challenging, depending on configuration) IPs that exceed a defined threshold within a 5-minute rolling window. In this scenario, the malicious traffic is distributed acrosshundreds of IPsin two countries, and the application still needs to remain available globally for legitimate users. A rate-based rule provides fast, targeted throttling that reduces abusive request patterns without permanently blocking entire geographies. This aligns with “quickly limit” while minimizing collateral impact.

Blocking both countries with a geo match rule (Option B) would likely block legitimate users located in those countries, which violates the requirement. Security groups (Options C and D) cannot natively enforcegeographicfiltering, and they are not well suited for large, rapidly changing sets of public source IPs at the application layer. Additionally, WAF operates at layer 7 with richer matching (rate limiting, URI/header patterns, bot controls), which is the appropriate control point when the ALB already has a web ACL associated. Therefore, implementing an AWS WAFrate-basedrule is the most effective and least disruptive immediate mitigation.

AWS CloudTrail provides authoritative records of KMS key creation, origin, and usage. Enabling log file validation ensures tamper detection. S3 Object Lock in compliance mode enforces immutability, which is a core audit requirement cited in AWS Certified Security – Specialty materials.

CloudWatch and DynamoDB do not provide immutable storage guarantees suitable for compliance evidence.

Referenced AWS Specialty Documents:

AWS Certified Security – Specialty Official Study Guide

AWS CloudTrail Log File Validation

Amazon S3 Object Lock

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

AWS WAF logs capturedetailed request-level information, including source IP address, request URI, headers, and rule evaluation results. According to the AWS Certified Security – Specialty documentation, AWS WAF logging is acritical detection controlwhen application-level attacks are suspected, especially when host-based logs are unreliable or can be erased by attackers.

By configuring the AWS WAF web ACL to send logs toAmazon Data Firehose, the company ensures that all future requests are centrally captured and delivered to a durable storage service such as Amazon S3. UsingAmazon Athena, the security team can query these logs to identify requests targeting specific application paths such as new-user-creation.php and extract the originating client IP addresses.

Option A is incorrect because VPC Flow Logs operate at the network layer and do not capture HTTP request paths. Option B is invalid because ALBs do not support CloudWatch agents. Option C is viable but introduces additional operational complexity and cost, making it less appropriate than the native WAF logging solution.

AWS documentation highlightsAWS WAF logging combined with Athenaas a best practice for forensic analysis and attacker identification.

AWS Certified Security – Specialty Official Study Guide

AWS WAF Logging Documentation

Amazon Athena User Guide

AWS Detection and Monitoring Best Practices

A credential stuffing attack at the ALB is aLayer 7problem and is best mitigated withAWS WAF. The attacker is distributed across many IPs, so blocking by IP in a security group (Option B) is ineffective and operationally heavy. A CloudWatch alarm (Option A) only alerts; it does not block or mitigate requests.

Because the malicious traffic uses a distinctive, knownUser-Agentstring associated with a mobile device emulator, AWS WAF can quickly reduce the attack by inspecting the User-Agent header and blocking matching requests. This approach is targeted: it blocks the identified automated attack pattern while allowing legitimate users who do not present that emulator User-Agent to continue logging in. The WAF rule can be deployed immediately on the existing ALB-associated web ACL and can be further refined (for example, applied only to /login paths, combined with rate-based rules, or integrated with Bot Control) to minimize false positives.

Option D is risky because “allow only legitimate user agents” is brittle: user agents are diverse and change frequently, and a strict allow-list can accidentally block real users. Therefore, a WAF custom block rule for the known malicious User-Agent string is the correct solution.

To keep S3 accessoff the public internet, the standard AWS approach is to use anAmazon S3 gateway VPC endpoint(AWS PrivateLink for S3 is not used; S3 uses gateway endpoints). A gateway endpoint adds routes in the VPC route tables so traffic destined for S3 stays on the AWS backbone network rather than traversing an internet gateway, NAT gateway, or public IP paths. This satisfies the “cannot send traffic over the public internet” requirement while allowing the application in Account A to reach S3 in the same Region.

Cross-account bucket access is controlled byIAM and the S3 bucket policy, not by networking between the two accounts’ VPCs. The bucket resides in S3 (a regional service), not inside Account B’s VPC, so connecting VPC-to-VPC (peering, transit gateway, VPN) does not inherently provide private access to S3. Those options would add complexity and still typically require internet/NAT unless S3 endpoints are used.

With the gateway endpoint in Account A, the application can privately reach S3, and because permissions are already granted to write to the bucket in Account B, the write operations will succeed without public internet routing.

CloudTrail trails can be configured as eithersingle-Regionormulti-Region. A single-Region trail delivers events only for the Region in which it is created; when the company begins using additional Regions, those events will not be logged to the existing S3 destination unless the trail is updated. The least operational overhead is tomodify the existing trailand enablemulti-Regionlogging (that is, configure the trail to “apply to all Regions”). This preserves the current S3 bucket destination, encryption settings, log file validation configuration, IAM roles, and any integrations that already depend on the existing trail name and S3 prefix structure.

Creating a new trail (Options A or C) increases overhead because the engineer would need to manage multiple trails or migrate downstream processes (alerting, Athena tables, SIEM ingestion, retention policies, and lifecycle rules). Option B is not how CloudTrail works—S3 notifications do not cause CloudTrail to collect events from other Regions; CloudTrail must be configured to generate and deliver those logs. Therefore, updating the existing trail to be multi-Region is the simplest and most maintainable fix.

The threat is client ID manipulation to break authorization boundaries. The strongest control is tobind the MQTT client identity to the authenticated device identity(the Thing) rather than trusting arbitrary client IDs provided by the client. Using theThing name as the client ID(Option A) removes ambiguity and makes the identifier predictable and tied to a registered identity.

On the authorization side, AWS IoT Core policies can use policy variables. Allowing iot:Connect only when the resource matches client/${iot:Connection.Thing.ThingName} (Option E) ensures the connection is permittedonlyif the client ID exactly equals the authenticated Thing name from the TLS certificate/Thing principal context. This prevents attackers from injecting special characters or choosing a different client ID to escalate access, because the policy evaluation ties the allowed client resource to the Thing identity, not the attacker-controlled string.

Option D is weaker because it effectively allows whatever client ID is presented (it matches the same value the client supplies), so it does not prevent crafted client IDs from being used. Option C is unrelated to the described MQTT connect authorization (and references an action not aligned with the scenario). Option B is an application-side check and can be bypassed by a malicious client; enforcement must be at AWS IoT Core policy level.