S3 ListObjects Access Denied: Add s3:GetObject Permission
A developer is troubleshooting an issue where an IAM user cannot perform 's3:ListBucket' on a bucket. Which THREE factors could cause this denial?
⚠ Common exam trap
Candidates often forget that a permissions boundary acts as a maximum permission limit. If an action (like s3:ListBucket) is not explicitly allowed in the permissions boundary, the user cannot perform that action, even if their identity-based IAM policy explicitly allows it.
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
✓
An explicit deny statement in the bucket policy.
Option B is correct because an explicit Deny in a bucket policy always overrides any Allow in an identity-based policy, so a Deny on s3:ListBucket would block the user regardless of other permissions. Option D is correct because a permissions boundary sets the maximum permissions an IAM user can have; if s3:ListBucket is not within the boundary, the effective permissions cannot include it even if an identity policy allows it. Option E is correct because s3:ListBucket must be explicitly granted in an identity-based policy (or another applicable policy) for the user to list the bucket, and its absence results in an implicit deny. Option A is not correct because S3 bucket access is not restricted by the user's default region; region only affects endpoint routing, not authorization. Option C is not correct because KMS encryption affects access to object data via kms:Decrypt, not the s3:ListBucket permission itself.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The bucket is in a different region than the user's default region.
Why it's wrong here
While S3 buckets are provisioned within a specific AWS region, IAM permissions are evaluated globally across all regions where a principal might attempt to access resources. The region where a user's default settings are configured, or the region where the S3 bucket resides, does not inherently restrict or deny IAM permissions for S3 actions like s3:ListBucket. Access is determined solely by the applicable IAM and resource policies, irrespective of regional differences.
- ✓
An explicit deny statement in the bucket policy.
Why this is correct
AWS IAM policy evaluation logic dictates that an explicit Deny statement always overrides any Allow statements, regardless of where the Allow is defined (e.g., in the user's identity-based policy). If the S3 bucket policy contains an explicit Deny for the s3:ListBucket action for the specific user or a group they belong to, this Deny will take precedence and prevent the user from listing the bucket's contents, even if their IAM policy allows it.
- ✗
The bucket is encrypted with AWS KMS.
Why it's wrong here
AWS KMS encryption primarily protects the data at rest within S3 objects, encrypting the object content itself. However, the s3:ListBucket action is a bucket-level permission that allows an IAM principal to view the metadata of objects within a bucket, such as their names and sizes, but not their actual encrypted content. Therefore, KMS encryption on the objects does not inherently prevent or deny the ability to list the contents of the bucket.
- ✓
The user has a permissions boundary that does not include s3:ListBucket.
Why this is correct
A permissions boundary sets the maximum permissions an IAM user can have. If the boundary does not include s3:ListBucket, the user cannot perform that action, even if their IAM policy allows it. This is a valid cause of denial.
- ✓
The user's IAM policy does not include s3:ListBucket.
Why this is correct
IAM policies are the primary mechanism for defining the permissions granted to an IAM user, group, or role. For an IAM user to successfully perform the s3:ListBucket action, their attached identity-based IAM policy must explicitly include this action within an Allow statement. If the s3:ListBucket action is absent from all applicable IAM policies, the user will be implicitly denied permission to list the bucket's contents, resulting in an access denied error.
Quick reference
AWS S3 Storage Class Comparison
| Storage Class | Min Duration | Retrieval | Use Case |
|---|---|---|---|
| S3 Standard | None | Immediate | Frequently accessed data |
| S3 Standard-IA | 30 days | Immediate | Infrequent access, rapid retrieval |
| S3 One Zone-IA | 30 days | Immediate | Non-critical infrequent data |
| S3 Intelligent-Tiering | None | Immediate–hours | Unknown or changing access patterns |
| S3 Glacier Instant | 90 days | Milliseconds | Archive with instant retrieval |
| S3 Glacier Flexible | 90 days | Minutes–hours | Archive, flexible retrieval |
| S3 Glacier Deep Archive | 180 days | Hours | Long-term compliance archive |
Go deeper
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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