An Empty S3 Bucket Can Make Your AWS Bills Explode

In the world of cloud computing, Amazon Web Services (AWS) is a giant that offers a wide range of services that cater to various needs, from storage to computation.

Among these services, AWS S3 (Simple Storage Service) is a trendy choice for data storage, known for its durability, availability, and scalability.

However, a recent incident highlights a lesser-known risk associated with S3 buckets that could lead to unexpectedly high charges on your AWS bill.

A few weeks ago, Maciej Pocwierz was working on a Proof of Concept (PoC) for a document indexing system for a client who created a single S3 bucket in the AWS eu-west-1 region.

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The intention was simple: upload some files for testing. However, within just two days, the developer faced a shocking AWS bill of over $1,300.

The billing console revealed nearly 100,000,000 S3 PUT requests had been executed against this newly created bucket in a single day.

This has sparked discussions regarding Denial-of-Wallet attacks, where malicious actors can cause significant expenses for bucket owners by making unauthorized requests.

Investigation and Discovery

Initially baffled by the massive number of requests, the developer turned to AWS CloudTrail, which provides logs for tracking user activity and API usage.

Maciej Pocwierz said that enabling CloudTrail made it evident that thousands of write requests were being sent to the S3 bucket from multiple external AWS accounts.

Further investigation revealed that a popular open-source backup tool had a default configuration that inadvertently pointed to the developer’s S3 bucket.

Every instance of this tool deployed with the default settings attempted to store its backups in the developer’s bucket, leading to a flood of PUT requests.

Bucket Naming and Security

This incident underscores the importance of carefully choosing the names of S3 buckets.

Using common names can lead to conflicts or unintended access if other users mistakenly or maliciously target the bucket.

To avoid such issues, it is advisable to use unique, non-descriptive names for S3 buckets.

Monitoring and Alerts

AWS users must monitor their usage and set up billing alerts. AWS provides tools like CloudWatch and Budgets that can send alerts when usage patterns change dramatically or when costs exceed certain thresholds. This can be a lifesaver in preventing billing surprises.

Understanding AWS Free Tier and Billing

Users must understand the limits of the AWS Free Tier and how billing works. S3 charges are based on storage used, number of requests, and data transferred.

Even if the stored data is minimal, many requests or large data transfers can result in significant charges.

While AWS S3 is a powerful tool for storage, the incident serves as a reminder of the potential financial risks associated with misconfigurations and security oversights.

Users must take proactive steps to secure their resources, monitor their usage, and understand their billing.

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