AWS CDK Flaw Exposes 1% of Users to Potential Account Takeover Risk

October 30, 2024

A significant security flaw has been discovered in the Amazon Web Services (AWS) Cloud Development Kit (CDK), an open-source framework that enables infrastructure as code (IaC). The vulnerability revolves around predictable naming patterns for staging S3 buckets created during the CDK bootstrapping process. This flaw could potentially allow attackers to perform name-squatting, leading to a complete account takeover under certain conditions, posing serious risks to users.

Discovery and Impact of the Flaw

Details of the Security Flaw

In a comprehensive analysis by security firm Aqua, this flaw was identified in CDK versions v2.148.1 and earlier. Around 1% of CDK users are impacted by this issue, as per AWS. The crux of the problem lies in the staging S3 bucket, generated automatically during CDK bootstrapping. This bucket’s naming convention follows a predictable format: “cdk-{qualifier}-assets-{account-ID}-{Region}”. The default qualifier “hnb659fds” is seldom customized by users. Consequently, if an attacker gains access to the user’s AWS Account ID and deployment region, the bucket’s name becomes easily predictable, making it susceptible to name-squatting. Malicious actors can then create the bucket themselves, resulting in a denial of service (DoS) attack by preventing legitimate users from generating their own staging bucket.

Further exacerbating the situation, the risk of a DoS attack can escalate to a full account takeover. If the compromised CDK writes and reads data, attackers can manipulate data within the CloudFormation template from their controlled staging S3 bucket. This enables them to execute malicious activities within the victim’s AWS account. The predictability of bucket names thus opens a vulnerability pathway that cybercriminals can exploit for more damaging impacts than simple disruption.

AWS Response and Mitigation Efforts

To mitigate this critical vulnerability, AWS has taken several measures. They have updated their documentation to emphasize the importance of customizing the CDK bootstrapping process, particularly changing the default “qualifier.” Starting from CDK version v2.149.0, AWS introduced a safeguard within the bootstrap FilePublishRole, preventing the CDK from writing data to buckets that are not owned by the initiating account. These steps aim to limit the potential attack vectors and bolster the security of AWS CDK implementations.

However, despite these fixes and recommendations, older bootstraps (CDK versions v2.148.1 or earlier) remain vulnerable unless they are explicitly reconfigured. This necessitates that users update and secure their setups meticulously to prevent any potential breaches. Aqua labels this flaw under its “Bucket Monopoly” attack methodology, which includes similar critical vulnerabilities in other AWS services such as CloudFormation, Glue, EMR, SageMaker, ServiceCatalog, and CodeStar. Addressing these vulnerabilities is essential for maintaining robust security postures in cloud environments.

Broader Implications and Recommendations

Industry-Wide Impact

The discovery of this flaw extends beyond just the AWS CDK and touches on broader security concerns within the cloud infrastructure domain. As more organizations leverage cloud services for their operational needs, they become increasingly vulnerable to sophisticated cyber attacks. This particular vulnerability serves as a cautionary tale about the interconnected nature of cloud services and the cascading impact that a single security flaw can have. It also raises questions about default settings provided by cloud service providers, urging users to customize these settings vigilantly.

Moreover, the flaw’s existence underscores the need for ongoing vigilance in cloud security practices. Organizations must routinely audit their cloud configurations and keep up with the latest security best practices. AWS’s proactive measures and the release of updated tools indicate a commitment to user security, but the onus is also on the end-users to implement these recommendations diligently. Ignoring such critical updates can render the most secure cloud environments vulnerable to exploitation.

Future Security Measures

A critical security vulnerability has been identified in the Amazon Web Services (AWS) Cloud Development Kit (CDK), an open-source tool designed for infrastructure as code (IaC). This flaw centers on the predictable naming conventions for staging S3 buckets that are automatically generated during the CDK bootstrapping process. Due to these predictable patterns, malicious actors could potentially exploit this loophole through a technique known as name-squatting. Name-squatting involves creating buckets with these predictable names before legitimate users do, thereby intercepting data and potentially leading to a complete takeover of the AWS account, given the right conditions. This issue presents a substantial risk to users who rely on AWS CDK for managing their cloud infrastructure. Security experts and AWS users alike are now urged to review their CDK configurations and implement additional security measures to mitigate this threat. AWS has been notified of this vulnerability, and users are encouraged to stay updated with any patches or advisories released by the platform to address these security concerns effectively.

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