Predictable S3 Bucket Names Exposed Six AWS Services to Cross-Account Attacks

Aqua Security researchers disclosed vulnerabilities in six AWS services involving predictable, automatically generated Amazon S3 bucket names. Discovered in February 2024, the “Shadow Resources” attack vector allowed attackers to register expected bucket names before legitimate deployments and, under vulnerable workflows, cause AWS services to use attacker-controlled storage. Potential consequences included data exposure, code or template manipulation, denial of service, and account takeover. The researchers’ “Bucket Monopoly” technique extended this approach across unused AWS regions to increase the likelihood of intercepting future deployments. The report did not establish malicious exploitation in the wild.

AWS remediated the affected workflows in CloudFormation, Glue, EMR, SageMaker, and Service Catalog. It considered CodeStar addressed through restrictions preventing new customers from creating projects ahead of the service’s planned retirement. Organizations should still audit custom and open-source deployment workflows for predictable bucket names and assumptions about storage ownership. Recommended safeguards include validating bucket ownership, using unpredictable names, and enforcing least-privilege, account-scoped access. AWS guidance on S3 bucket policies and cross-account policy evaluation provides a basis for reviewing both identity- and resource-based permissions so that deployment roles cannot inadvertently trust attacker-controlled buckets.