Did you know your S3 bucket name isn’t just a label? It’s a low-key DNS hostname that can become a security risk. This isn’t a drill.
This isn’t theoretical. And no, AWS won’t save you by default.
First, a Little S3 Bucket Lore
S3 buckets exist in a flat global namespace. That means if you create mycompany-assets, no one else on the entire internet ever can.
Now imagine that back in 2015, some engineer at your org created company-cdn. It served files via S3 static website hosting. At some point, the bucket was deleted. But the DNS name (company-cdn.s3.amazonaws.com) remained hardcoded in places — old app builds, outdated docs, maybe even some third-party integrations.
Now imagine that an attacker swoops in and registers that exact bucket name and starts serving malicious content under your trusted subdomain.
S3 Bucket Hijacking: The World’s Dumbest Smart Attack
Let’s walk through the playbook of a pretty common — and embarrassingly simple — attack:
- An attacker finds references to a now-nonexistent S3 bucket in your code, mobile app, or CDN config.
- They register that exact bucket name in their AWS account.
- They upload malicious files — maybe a fake login page, a JavaScript snippet, or an executable disguised as an image.
- Users, apps, or search engines still resolving the old domain start hitting the attacker’s bucket, completely unaware.
If your apps or front-end are referencing those buckets via DNS (and many do), it’s game over. You’ve just been subdomain jacked.
But I Don’t Use S3 Static Website Hosting.
You still might be vulnerable. Here’s how bucket names can bite you even when you’re “doing it right”:
- URL-style addressing: S3 URLs like https://mycompany-assets.s3.amazonaws.com/file.jpg rely on your bucket name as part of the hostname.
- Misconfigured CNAMEs or Route 53 records: Your DNS could be pointing to a bucket that no longer exists.
- Browser caching + prefetching: Even if you’re not using a bucket now, some user agent somewhere might still be requesting it.
And if you’re using a bucket name that resembles something generic (media-cdn-prod, static-files, etc.), you’d better believe bots are scanning for those and trying them.
Why Your Bucket Name Matters
You wouldn’t name your domain with a capital I instead of an L, right? So why would you name your S3 bucket something that could
- Be easily typo-squatted
- Collide with another company’s convention
- Looks like a legitimate service (cdn-facebook-prod, anyone?)
- Confuse internal vs. external visibility
Bucket names are often copied and pasted across environments, used in Terraform modules, and baked into CI/CD scripts. A poorly chosen name can end up in places you didn’t plan , and those places often don’t get security reviews.
So What Do You Do About It?
1. Use unique, brand-specific, non-generic bucket names.
Avoid names like static-assets, media-cdn, or prod-files. Make it something like acme-prod-assets-3928d — not cute, but harder to hijack or collide with.
2. Monitor DNS and bucket usage.
Use tools like AWS Config, GuardDuty, or external DNS monitoring to catch when things start pointing to buckets that no longer exist.
3. Never delete a bucket that’s referenced externally without locking down the DNS.
Either remove all DNS records pointing to it or create a placeholder bucket that returns a 403.
4. Turn off public access settings by default.
Seriously. This one’s a freebie. AWS now blocks public access by default — keep it that way unless you know what you’re doing.
5. Audit your buckets like you audit IAM roles.
Don’t treat storage like an afterthought. Just because it’s “just images” doesn’t mean it’s harmless.
S3 buckets aren’t just dumb storage containers — they’re internet-facing resources with real-world security implications. And their names? They’re hostnames, branding elements, and sometimes attack vectors all rolled into one.
If you wouldn’t casually buy a domain like mycorp-files.net without thinking through the implications, don’t casually name your S3 buckets, either.
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