Question 178 of 1,748
Infrastructure SecurityeasyMultiple ChoiceObjective-mapped

S3 Bucket Policy Granting EC2 Permissions — Cross-Service Resource-Based Policies

This SCS-C02 practice question tests your understanding of infrastructure security. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.

Exhibit

Refer to the exhibit.

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Principal": {
        "AWS": "arn:aws:iam::123456789012:role/CrossAccountRole"
      },
      "Action": [
        "ec2:DescribeInstances",
        "ec2:StartInstances",
        "ec2:StopInstances"
      ],
      "Resource": "*",
      "Condition": {
        "StringEquals": {
          "aws:SourceAccount": "123456789012"
        }
      }
    }
  ]
}

Refer to the exhibit. A security engineer is reviewing an IAM policy attached to an S3 bucket. What does this policy allow?

Exhibit

Refer to the exhibit.

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Principal": {
        "AWS": "arn:aws:iam::123456789012:role/CrossAccountRole"
      },
      "Action": [
        "ec2:DescribeInstances",
        "ec2:StartInstances",
        "ec2:StopInstances"
      ],
      "Resource": "*",
      "Condition": {
        "StringEquals": {
          "aws:SourceAccount": "123456789012"
        }
      }
    }
  ]
}

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

Allows a role to describe, start, and stop EC2 instances in the account.

The policy allows a specified role (from the same account) to perform EC2 actions: DescribeInstances, StartInstances, and StopInstances. Even though the policy is attached to an S3 bucket, AWS resource-based policies can grant permissions to any service action, and the principal is a role ARN in the same account, enabling the role to manage EC2 instances.

Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

  • Allows a role from another account to describe, start, and stop EC2 instances in the current account.

    Why it's wrong here

    The principal is a role in the same account (123456789012), not a different account.

  • Allows a role to describe, start, and stop EC2 instances in the account.

    Why this is correct

    The policy grants EC2 actions to the specified role.

    Related concept

    Read the scenario before looking for a memorised answer.

  • Allows all IAM users in the account to view EC2 instances.

    Why it's wrong here

    The principal is a specific role, not all users.

  • Allows an IAM user to list and manage objects in the S3 bucket.

    Why it's wrong here

    The actions are EC2, not S3.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is that candidates may assume the policy only applies to S3 actions because it is attached to an S3 bucket, but AWS allows resource-based policies to grant permissions for any service action, leading to confusion about the actual scope of the policy.

Detailed technical explanation

How to think about this question

The policy uses a resource-based policy attached to an S3 bucket, but the actions are EC2 actions, which is unusual but valid—resource-based policies can grant permissions for actions on other services if the principal is allowed. The ARN in the Principal element specifies a role in the current account, enabling that role to perform EC2 actions on instances in the same account. This pattern is often used for cross-service access where an S3 bucket policy grants EC2 management permissions to a specific role for automation or monitoring purposes.

KKey Concepts to Remember

  • Read the scenario before looking for a memorised answer.
  • Find the constraint that changes the correct option.
  • Eliminate answers that are true in general but not in this case.

TExam Day Tips

  • Watch for words such as best, first, most likely and least administrative effort.
  • Review why wrong options are wrong, not only why the correct option is correct.

Key takeaway

Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Real-world example

How this comes up in practice

A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.

Quick reference

AWS S3 Storage Class Comparison

Storage ClassMin DurationRetrievalUse Case
S3 StandardNoneImmediateFrequently accessed data
S3 Standard-IA30 daysImmediateInfrequent access, rapid retrieval
S3 One Zone-IA30 daysImmediateNon-critical infrequent data
S3 Intelligent-TieringNoneImmediate–hoursUnknown or changing access patterns
S3 Glacier Instant90 daysMillisecondsArchive with instant retrieval
S3 Glacier Flexible90 daysMinutes–hoursArchive, flexible retrieval
S3 Glacier Deep Archive180 daysHoursLong-term compliance archive

What to study next

Got this wrong? Here's your next step.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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FAQ

Questions learners often ask

What does this SCS-C02 question test?

Infrastructure Security — This question tests Infrastructure Security — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: Allows a role to describe, start, and stop EC2 instances in the account. — The policy allows a specified role (from the same account) to perform EC2 actions: DescribeInstances, StartInstances, and StopInstances. Even though the policy is attached to an S3 bucket, AWS resource-based policies can grant permissions to any service action, and the principal is a role ARN in the same account, enabling the role to manage EC2 instances.

What should I do if I get this SCS-C02 question wrong?

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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Last reviewed: Jul 4, 2026

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This SCS-C02 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the SCS-C02 exam.