## The “LambdaChain” Exploit: How a Single IAM Misconfiguration Led to a Full AWS Account Takeover
**A Step-by-Step Tutorial from an Attacker’s Perspective for Cloud Developers and Cloud Security Engineers**
In the world of cloud security, we often talk about the principle of least privilege. We strive to create IAM policies that are as granular as possible, giving our applications and services only the permissions they need to do their jobs. But in the complex and interconnected world of a modern serverless architecture, it only takes one small misconfiguration, one overly permissive IAM role, to unravel the entire security posture of your AWS account.
This article will walk you through the “LambdaChain” exploit, a step-by-step attack that demonstrates how a single, seemingly innocuous IAM misconfiguration in a Lambda function can be used to achieve a full AWS account takeover. We’ll look at the attack from the perspective of the adversary, showing you how they can pivot from one service to another, chaining together a series of small permissions to ultimately achieve administrative control of the account.
### The Setup: A Single, Overly-Permissive Lambda Function
Our attack begins with a single, overly-permissive Lambda function. This function is designed to process user uploads to an S3 bucket, and in the interest of expediency, the developer has given it a broad set of permissions that go far beyond what it actually needs. The IAM role attached to the function allows it to not only read and write to the S3 bucket, but also to assume other roles, list all of the IAM roles in the account, and access other services like DynamoDB and Secrets Manager.
This is a common scenario in many organizations. Developers are often under pressure to deliver new features quickly, and they may not have the time or the expertise to create a perfectly crafted IAM policy. But as we’ll see, this small shortcut can have devastating consequences.
### The Attack Chain: From Lambda to Admin
Now that we have our target, let’s walk through the attack chain, step-by-step, from the perspective of the attacker.
**1. Gaining a Foothold:** The first step is to gain a foothold in the Lambda function itself. This can be achieved through a variety of methods, such as a file upload vulnerability, a command injection flaw, or a deserialization bug. Once we have remote code execution (RCE) in the Lambda, we can begin to explore the environment and to enumerate the permissions of the attached IAM role.
**2. Enumerating Permissions:** With our foothold in the Lambda, we can now use the AWS CLI to enumerate the permissions of the attached IAM role. We can use the `aws iam list-roles` command to get a list of all the roles in the account, and we can use the `aws iam get-role-policy` command to get the details of each role’s policy.
**3. Pivoting to Other Services:** Now that we have a list of all the roles in the account, we can start to look for opportunities to pivot to other services. We can use the `aws sts assume-role` command to assume any role that our current role is allowed to assume, and we can then use the permissions of that new role to access other services.
**4. The Path to Admin:** In our scenario, the Lambda’s IAM role has the permission to assume a role that, in turn, has the permission to read from a DynamoDB table. This table contains the credentials for a database, which we can then use to access a Secrets Manager secret that contains the credentials for an administrative user. With these credentials in hand, we have achieved a full account takeover.
### Preventing the LambdaChain Exploit
The LambdaChain exploit is a powerful and devastating attack, but it’s also a preventable one. Here are some key steps you can take to protect your AWS account from this type of attack:
* **Apply the Principle of Least Privilege:** This is the most important and most effective defense against the LambdaChain exploit. By creating granular IAM policies that give your Lambda functions only the permissions they need to do their jobs, you can significantly reduce the attack surface and prevent an attacker from being able to pivot to other services.
* **Use Automated IAM Scanning Tools:** There are a number of open-source and commercial tools that can be used to scan your IAM policies for misconfigurations and to identify any overly permissive roles.
* **Implement Service Control Policies (SCPs):** SCPs are a powerful feature of AWS Organizations that can be used to set a baseline of security for all of your AWS accounts. By using SCPs to deny access to sensitive services like IAM and Secrets Manager, you can prevent an attacker from being able to escalate their privileges even if they are able to compromise a single Lambda function.
### Conclusion: The Butterfly Effect of IAM Misconfigurations
The LambdaChain exploit is a stark reminder of the butterfly effect of IAM misconfigurations. A single, seemingly insignificant error can have a cascading effect that can ultimately lead to a full account takeover. By taking a defense-in-depth approach that combines the principle of least privilege with automated scanning and a robust set of preventative controls, you can protect your AWS account from this and other emerging threats. The security of your serverless architecture is only as strong as your weakest IAM policy, and in the world of the cloud, a single weak link can be all an attacker needs.
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