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Question 671 of 1,616

Security →mediumMultiple ChoiceObjective-mapped

Quick Answer

The correct approach is to use cross-account IAM roles with STS AssumeRole, which generates temporary credentials for secure S3 access. This method works by having the source account create an IAM role with a trust policy that allows the external user’s account to assume it, while the role’s permissions policy grants specific S3 bucket actions. The external user then calls the STS AssumeRole API to receive temporary access keys, a secret key, and a session token that automatically expire—typically after one hour, up to a maximum of twelve hours—eliminating the risk of exposed long-term credentials. On the AWS Certified Developer Associate DVA-C02 exam, this scenario tests your understanding of identity federation and least privilege; a common trap is choosing pre-signed URLs (which grant object-level access but require the requesting account to already have permissions) or access key sharing (which violates security best practices). Remember the mnemonic “STAR” for Secure Temporary Access via Roles: the external user must first be authenticated in their own account, then assume the role in the target account to receive the temporary token.

DVA-C02 Security Practice Question

This DVA-C02 practice question tests your understanding of 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.

A developer needs to grant temporary access to an Amazon S3 bucket for a user from a different AWS account. The developer wants to use the most secure method that does not require sharing long-term credentials. Which approach should the developer take?

Question 1mediummultiple choice

Full question →

A
Create an IAM user in the developer's account and share the access keys
Why wrong: This would require sharing long-term access keys, which is a security risk. It does not use temporary credentials and violates the principle of least privilege.
B
Use S3 bucket policy with a condition for the external account's IAM user
Why wrong: While a bucket policy can grant access to an external IAM user, that user still uses long-term credentials. This is not as secure as using temporary credentials via role assumption.
C
Use cross-account IAM roles with STS AssumeRole
This allows the external user to assume a role in the developer's account, obtaining temporary credentials. It does not require sharing long-term keys and provides fine-grained control.
D
Use S3 access control lists (ACLs) with the external user's canonical user ID
Why wrong: ACLs are a legacy permission mechanism and require the external user's canonical ID, which involves sharing long-term identifiers. They are less secure and not recommended for cross-account access.

Full breakdown with real-world context →

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

✓

Use cross-account IAM roles with STS AssumeRole

Option C is correct because using cross-account IAM roles with AWS Security Token Service (STS) AssumeRole allows the external user to obtain temporary, limited-privilege credentials without sharing any long-term access keys. This approach follows the principle of least privilege and eliminates the risk of exposed static credentials, as the temporary credentials automatically expire after a configurable duration (default 1 hour, max 12 hours).

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.

✗
Create an IAM user in the developer's account and share the access keys
Why it's wrong here
This would require sharing long-term access keys, which is a security risk. It does not use temporary credentials and violates the principle of least privilege.
✗
Use S3 bucket policy with a condition for the external account's IAM user
Why it's wrong here
While a bucket policy can grant access to an external IAM user, that user still uses long-term credentials. This is not as secure as using temporary credentials via role assumption.
✓
Use cross-account IAM roles with STS AssumeRole
Why this is correct
This allows the external user to assume a role in the developer's account, obtaining temporary credentials. It does not require sharing long-term keys and provides fine-grained control.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use S3 access control lists (ACLs) with the external user's canonical user ID
Why it's wrong here
ACLs are a legacy permission mechanism and require the external user's canonical ID, which involves sharing long-term identifiers. They are less secure and not recommended for cross-account access.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is that candidates often confuse S3 bucket policies with cross-account access, thinking a bucket policy alone can grant temporary credentials, when in fact bucket policies only authorize access based on the requester's existing (long-term) credentials and do not issue temporary tokens.

Detailed technical explanation

How to think about this question

Under the hood, the AssumeRole API call returns a temporary security token (AccessKeyId, SecretAccessKey, SessionToken) with a defined expiration, which the external user's application uses to sign S3 requests. The trust policy on the IAM role in the developer's account must explicitly grant the external account's IAM user or role permission to assume the role, and the external user must call STS:AssumeRole with the role ARN. A real-world scenario is a third-party data processor that needs to upload files to your S3 bucket for a limited time; using cross-account roles ensures that even if the external account is compromised, the temporary credentials cannot be used beyond their expiration.

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.

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 DVA-C02 question test?

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

What is the correct answer to this question?

The correct answer is: Use cross-account IAM roles with STS AssumeRole — Option C is correct because using cross-account IAM roles with AWS Security Token Service (STS) AssumeRole allows the external user to obtain temporary, limited-privilege credentials without sharing any long-term access keys. This approach follows the principle of least privilege and eliminates the risk of exposed static credentials, as the temporary credentials automatically expire after a configurable duration (default 1 hour, max 12 hours).

What should I do if I get this DVA-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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Same concept, more angles

2 more ways this is tested on DVA-C02

These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.

Variation 1. A company wants to grant a third-party vendor access to an Amazon S3 bucket in the company's AWS account. The vendor has their own AWS account. The company requires the vendor to include a unique identifier in each request to verify their identity before granting access. Which policy element should the company include in the S3 bucket policy?

hard

✓ A.Condition with sts:ExternalId
B.Condition with aws:SourceArn
C.Condition with aws:SourceAccount
D.Principal element with the vendor's AWS account ID

Why A: The `sts:ExternalId` condition key is specifically designed for scenarios where a third party (the vendor) needs to access AWS resources in your account, and you want to ensure that the vendor includes a unique identifier in each request. This prevents the confused deputy problem by requiring the vendor to pass the external ID in the `AssumeRole` call or directly in the request to S3 when using role-based access. By including this condition in the bucket policy, the company can verify that the request originates from the intended vendor and not from another entity trying to misuse the permissions.

Variation 2. A developer needs to grant an IAM user access to an S3 bucket owned by another AWS account. Which method should be used?

easy

A.Create an IAM role in the bucket owner account and allow the user to assume it.
B.Create a new IAM user in the bucket owner account for the developer.
✓ C.Attach a bucket policy to the bucket that allows the user's IAM user ARN.
D.Add the user to a bucket ACL granting access.

Why C: Cross-account access requires a bucket policy in the account owning the bucket, granting access to the IAM user ARN from the other account.

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