AWS Cloud Development Kit flaw exposed accounts to full takeover, patch now available

Amazon Web Services (AWS) has patched a security flaw in its open-source Cloud Development Kit (CDK) that could have allowed attackers to hijack AWS user accounts. The vulnerability, identified by security researchers from Aqua Security, highlights how predictable S3 bucket naming structures could be exploited in specific scenarios, posing a critical threat to cloud infrastructure security.

About the AWS Cloud Development Kit Vulnerability

AWS's Cloud Development Kit (CDK) enables developers to design and provision cloud infrastructure using popular programming languages like Python, TypeScript, JavaScript, and Go.

However, Aqua Security researchers Ofek Itach and Yakir Kadkoda discovered a flaw within the CDK’s “bootstrapping” process, which is required to set up a new environment. During this process, CDK automatically creates identity and access management (IAM) roles, permissions, policies, and an S3 staging bucket to store assets for deployment.

The problem stems from the default naming convention of these CDK staging buckets, which could allow attackers to predict their names based on AWS account ID and region data. Known as "S3 Bucket Namesquatting," this vulnerability allows attackers to claim a predictable bucket name, preload it with malicious code, and wait for the target organization to unwittingly execute it.

If successful, the exploit would allow the attackers to execute various actions within the victim’s environment including data exfiltration. This could escalate to a full account takeover in the worst-case scenario, giving attackers administrative control of a target AWS account.

AWS Patch and Mitigation Recommendations

AWS has since issued a fix in CDK version v2.149.0, which includes updated protocols to prevent the exploitation of predictable bucket names. The update restricts asset uploads strictly to S3 buckets owned by the user’s account, blocking any unauthorized external access.

AWS says it notified users of this flaw, but action is still required for those who bootstrapped environments using earlier CDK versions.

Aqua Security advises users running CDK version 2.148.1 or earlier to upgrade to the latest version (v2.149.0 or higher) and re-run the cdk bootstrap command to secure their environments. If upgrading is impossible, Aqua suggests an alternative solution: applying an IAM policy condition to the FilePublishingRole. This additional step restricts unauthorized access to the role and enhances security. It’s similar to the AWS patch.

To further mitigate risks associated with predictable bucket names, Aqua recommends adopting unique hashes or random identifiers for S3 bucket names. This ensures they cannot be easily guessed or hijacked by malicious actors.

Takeaways for Cloud Security

Although AWS's patch addresses the vulnerability, this incident serves as a reminder to organizations to regularly audit and update their infrastructure and to be cautious with default configurations that may inadvertently expose them to attacks.