Unauthorized Access to Sensitive Files in AWS S3

Attackers frequently target cloud storage environments to harvest sensitive files that facilitate lateral movement and persistence. AWS S3 buckets are often misconfigured or over-privileged, leading to the exposure of configuration files (e.g., .aws/credentials, .env), SSH keys, and PEM/PuTTY private keys. This threat brief highlights the importance of monitoring S3 Data Events to detect when these high-value assets are accessed via 'GetObject' calls. Defenders should focus on identifying access by non-automation identities, as legitimate CI/CD pipelines and administrative tools may also retrieve these files. Ensuring that S3 Data Events are explicitly enabled in CloudTrail is a prerequisite for observability, as management plane events do not capture individual object access.

Impact

Successful retrieval of these credentials can lead to full compromise of the affected AWS identity, unauthorized access to underlying infrastructure, and potential exfiltration of proprietary data or source code. If the retrieved credentials are reused elsewhere, the impact extends beyond the immediate cloud environment to integrated third-party services and local development machines.

Recommendation

• Enable AWS S3 Data Events in CloudTrail to gain visibility into object-level operations.
• Implement and tune the provided Sigma-compatible detection logic to identify 'GetObject' events targeting sensitive file patterns.
• Audit S3 bucket policies for overly permissive access (e.g., public read or broad IAM permissions).
• Treat all retrieved credential files as compromised; rotate secrets and keys immediately upon detection of unauthorized access.
• Establish a baseline of authorized IAM roles and source IPs for S3 bucket access to reduce false positives from automated CI/CD processes.