GHSA-xx8w-mq23-29g4

Описание

Summary

When someone creates an access key, it inherits the permissions of the parent key. Not only for s3:* actions, but also admin:* actions. Which means unless somewhere above in the access-key hierarchy, the admin rights are denied, access keys will be able to simply override their own s3 permissions to something more permissive.

Credit to @xSke for sort of accidentally discovering this. I only understood the implications.

Details / PoC

We spun up the latest version of minio in a docker container and signed in to the admin UI using the minio root user. We created two buckets, public and private and created an access key called mycat and attached the following policy to only allow access to the bucket called public.

We then set an alias in mc: mcli alias set vuln http://localhost:9001 mycat mycatiscute

And checked whether policy works:

Looks good, we believe this is how 99% of users will work with access policies.

If I now create a file full-access-policy.json:

And then:

mycat has escalated its privileges to get access to the entire deployment:

Impact

A trivial privilege escalation unless the operator fully understands that they need to explicitly deny admin actions on access keys.

Patched