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Severity
High
Analysis Summary
A recently disclosed security flaw in Amazon Web Services (AWS) Cloud Development Kit (CDK) exposed users to potential account takeovers.
According to the researchers, this vulnerability stemmed from the predictable naming conventions used during the bootstrapping process, particularly for AWS Simple Storage Service (S3) buckets and Identity and Access Management (IAM) roles. This flaw allowed attackers to execute Bucket Monopoly attacks, compromising sensitive data. After responsible disclosure in June 2024, AWS patched the vulnerability in CDK version 2.149.0.
The issue arises from the bootstrapping process where essential AWS resources like S3 buckets and IAM roles are provisioned. By default, the naming convention for these resources follows a predictable pattern especially if users do not customize the "Qualifier" field which defaults to "hnb659fds." This predictability allows attackers to exploit unclaimed or deleted S3 buckets by creating their own buckets using the same name, potentially leading to partial denial-of-service (DoS) attacks and, in more severe cases, full account takeover.
The attack method called S3 Bucket Namesquatting enables adversaries to hijack CDK buckets and tamper with CloudFormation templates deployed by the victim's account. If the victim’s CDK has permission to read and write from the rogue bucket attackers could inject malicious code or administrative roles into the templates, thereby executing unauthorized actions in the victim’s AWS environment. Such exploitation could allow attackers to gain privileged access within the compromised account.
For the attack to succeed the adversary must first claim the predictable bucket name and configure it for public access. By manipulating CloudFormation templates uploaded by the victim's CDK attackers can insert backdoor admin roles enabling full control of the account. AWS has mitigated the vulnerability by ensuring assets are uploaded only to buckets within the account that initiated the bootstrap process and advised users to adopt unique qualifiers instead of default values.
In response to the findings, AWS has urged customers to update to the latest CDK version and re-run the bootstrap process. Users who deploy the CDK with older versions must update the tool and consider applying additional IAM policies to protect their accounts. The report emphasizes the importance of obscuring AWS account IDs, using unique bucket names, and enforcing scoped IAM policies to minimize security risks in cloud environments.
Impact
- Sensitive Data Theft
- Unauthorized Access
- Privilege Escalation
- Denial of Service
Remediation
- Ensure that you are using AWS CDK version 2.149.0 or later, as it contains the necessary fixes. If bootstrapping was done with an older version (v2.148.1 or earlier), re-run the bootstrap command after updating.
- During the bootstrapping process, avoid using the default qualifier ("hnb659fds"). Instead, specify a custom, unique qualifier to prevent attackers from predicting resource names like S3 buckets and IAM roles.
- Restrict permissions for IAM roles associated with the CDK (such as CloudFormationExecutionRole) by defining more granular policies. Avoid granting broad administrative privileges to these roles.
- Ensure that S3 bucket names are unique by incorporating random identifiers or hashes into the naming convention. This helps prevent bucket namesquatting attacks.
- Apply additional IAM policy conditions to the FilePublishingRole CDK role to restrict its actions to resources within the same AWS account, preventing unauthorized access or tampering by external entities.