S3 Misconfiguration Case Study - $10,000 Deep

Advanced Case Study: $10,000 for a Misconfigured S3 Bucket ​

Cloud misconfigurations are one of the richest veins for bug bounty hunters and security teams. This case study walks you through a real-style scenario: how a public S3 bucket was discovered, what sensitive secrets it contained, the real-world impact, and how the company and hunter handled it - ending in a $10,000 bounty.

The goal: learn concrete recon, verification, impact assessment, remediation, and hunting tips you can apply ethically in authorized scopes.

Recon Phase - Finding the Surface Area ​

The hunter started with standard asset discovery and subdomain enumeration to map the target’s surface:

subfinder -d company.com -o subdomains.txt

Output found a host: assets.company.com

A quick DNS lookup and passive reconnaissance suggested the hostname resolves to an Amazon S3 endpoint (common pattern: assets.company.com.s3.amazonaws.com or an alias to an S3 bucket). That’s a strong signal to check bucket accessibility.

Why this matters: Many orgs host static assets or backups in S3, and sometimes those buckets are left public by mistake. A public bucket can be a low-effort, high-impact find.

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Testing the Bucket - Confirming Public Access (Safe & Non-Destructive) ​

Always work within legal scope. In authorized programs you can attempt non-destructive checks like listing the bucket. The hunter used the AWS CLI to confirm:

aws s3 ls s3://company-bucket-name

The command returned a list of files - the bucket was public. To mirror the contents for local analysis in a lab environment, the hunter used:

aws s3 sync s3://company-bucket-name ./loot

Important: Only download bucket contents when legally allowed (bug bounty scope or explicit permission). If you're pentesting, follow the program rules and do not exfiltrate data beyond what is required for reporting.

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What He Found - From Images to Secrets ​

Inside the bucket the hunter found:

• product_images/ - benign assets
• invoices/ - customer billing PDFs (sensitive PII)
• config/production.env - critical secrets, e.g.:

DB_USER=admin
DB_PASS=SuperSecret123
AWS_ACCESS_KEY=AKIA****************
AWS_SECRET_KEY=*********************

A single .env with live credentials is often a jackpot. The presence of AWS access keys suggested potential for broader cloud takeover.

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Impact - From Files to Full Cloud Compromise ​

With the discovered AWS keys, attackers could:

• Spin up infrastructure using the victim’s cloud account (cost & abuse).
• Access databases using leaked DB credentials (data theft, modification).
• Discover internal services, pivot into private networks, or enumerate more secrets via IAM.
• Perform privilege escalation within the cloud by abusing exposed roles or policies.

This is critical severity: keys + production credentials = full compromise potential.

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Responsible Disclosure & Bounty Process ​

The hunter followed responsible disclosure:

1. Documented exact steps to reproduce (DNS, bucket path).
2. Provided screenshots and timestamps proving public access.
3. Highlighted sensitive files and potential impact (data exfil, account takeover).
4. Suggested immediate mitigations (make bucket private, rotate keys).

Company action:

• Fixed bucket ACL/config to private.
• Rotated all exposed credentials immediately.
• Performed a post-incident review and accepted the report.

Result: the company awarded a $10,000 bounty for the critical impact and clear remediation path.

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Lessons for Hunters - How to Hunt Cloud Bugs Ethically ​

• Always confirm scope. Only test assets in-scope for the program.
• Check storage services: S3, GCP buckets, Azure blobs — all can be misconfigured.
• Look for config files: .env, config.json, .aws/credentials, and backups often contain secrets.
• Automate carefully: Tools like s3scanner or cloud_enum help find buckets, but use them responsibly.

Example tools (ethical use only):

s3scanner --bucket company-bucket
# or cloud enumeration frameworks inside your lab

• Proof not pillage: Collect minimum proof needed for triage and reporting. Don’t exfiltrate or publish sensitive user data.

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Lessons for Companies - How to Prevent Catastrophic Misconfigurations ​

1. Make storage private by default. S3 buckets should not be public unless explicitly required.
2. Use IAM least-privilege. Avoid broad access keys; use roles with narrow permissions.
3. Enable MFA & key rotation. Automate rotation of static keys and prefer ephemeral credentials (STS).
4. Audit & monitor: Enable AWS Config rules, Security Hub, and CloudTrail alerts for public ACLs and credential usage anomalies.
5. Automated scanning: Integrate cloud misconfiguration checks in CI/CD pipelines and run periodic scans for public buckets.
6. Secrets management: Move secrets to managed stores like AWS Secrets Manager or Parameter Store; never commit secrets to repos.

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Detection & Incident Response - What to Do Immediately ​

If you discover a public bucket with secrets:

• Notify the asset owner via the program’s disclosure channel ASAP.
• Provide repro steps and evidence but avoid publishing sensitive content.
• Recommend immediate rotation of keys and revocation of compromised credentials.
• Suggest a forensic review of CloudTrail to check for unauthorized actions.
• Help with remediation scripts if you’re engaged as an authorized researcher.

Sample immediate mitigation commands (for admins):

# Make S3 bucket private (example)
aws s3api put-bucket-acl --bucket company-bucket-name --acl private

# Revoke suspect keys (rotate)
aws iam update-access-key --access-key-id AKIA... --status Inactive --user-name username

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Pro Tips for Hunters - Focus on Cloud to Stand Out ​

• Many researchers still focus on web app XSS/SQLi; cloud misconfigurations are less crowded and often yield higher bounties.
• Small buckets can hold big secrets - always check config and backup folders.
• Learn IAM, CloudTrail, and common cloud patterns - that knowledge converts a finding into a high-impact report.
• Automate slow reconnaissance but prioritize manual verification; responsible disclosure wins trust and higher payouts.

Final Thoughts - Small Mistakes, Huge Consequences ​

This case shows how a single misconfigured S3 bucket turned into a potential full-cloud compromise and a large bounty. For defenders, the lesson is clear: secure defaults, continuous monitoring, and fast response. For hunters, the opportunity is equally clear - cloud misconfigurations are high-impact, often under-tested, and highly remunerative when reported responsibly.