Public S3 buckets, open Google Cloud Storage, anonymous Azure Blob containers — data exposure via cloud object stores is the most-documented cloud breach class. The mechanism: customer flagged the storage as public (often accidentally or historically); data inside is sensitive; internet-facing enumeration finds it; leak.
Why this keeps happening
- Multiple ways to make storage public. AWS S3: bucket ACL, bucket policy, object ACL, individual object grants, “allUsers” in IAM — each independent setting can grant public access.
- Defaults changed over time. S3 pre-2018 allowed public by default; changed, but old buckets inherited old defaults.
- “Temporary” public sharing becomes permanent. File needs external sharing for one meeting; public flag set; never unset.
- Developer intentionally public. “It’s just test data” — turns out to be customer PII accidentally mixed in.
- Misunderstanding of scope. “Only people with link can access” — but link gets posted to GitHub → indexed.
Discovery workflows
# Bucket name prediction + enumeration
# Common patterns: company-backups, company-dev, company-prod, etc.
for name in company-backups company-prod company-dev company-reports; do
aws s3 ls s3://$name 2>/dev/null
done
# Tools:
# - bucket_finder
# - AWSBucketDump
# - GCPBucketBrute
# - Cloud_Enum (multi-cloud)
# Google dorks
site:amazonaws.com "COMPANY"
inurl:s3.amazonaws.com "Index of"
# GitHub / pastebin searches for exposed bucket URLs + credentials
# grayhatwarfare.com — publicly accessible S3 buckets searchableSpecific settings to audit
AWS S3:
- Block Public Access at account level (enable all four settings)
- Block Public Access at bucket level
- Bucket ACL — check for “AllUsers” or “AuthenticatedUsers” grants
- Bucket policy — Principal “*”
- Object ACLs (ugh — each object can be independently public)
- Pre-signed URLs with overly-long expiry
Azure Blob:
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