GHSA-5cj2-rqqf-hx9p

Описание

Summary

Predictable secret ID and lack of secret origin API enable confused deputy attacks on Juju workloads.

Details

A Juju application can create a secret and grant it to another integrated application (grantee).

When they do so, the secret owner has to communicate the secret id to the grantee.

The grantee, having received the secret id can load the secret content and perform operations on behalf of the secret owner.

However, today the grantee has no way to determine which granted secret belongs to which owner.

Instead the grantee relies on:

• being able to read the secret by id (secret was in fact granted, by some entity)
• secret id was received over a relation (the remote end of the relation is presumed to be secret owner)

Additionally, secret IDs are XID, which are predictable, here two secrets created by two distinct apps in the same K8s model close in time:

PoC

This allows for an IDOR attack where:

• actors:
  • a Good application (the owner of the Victim),
  • an Evil application, and
  • a Provider application (the Confused Deputy)
• relations: Good --- Provider, Evil --- Provider
• secrets: Good and Evil create Secrets, granting them to the Provider and communicate Secret IDs with the Provider.
• semantics: the Provider performs some operation on behalf of the Good/Evil using the Secret.
• weakness 1: Evil can guess the Secret ID that Good granted and communicated to Provider.
• weakness 2: Juju doesn't provide the Provider application the facility to verify the provenance of the Secret IDs.
• exploit: Evil passes Good's secret id to Provider.
• bypass: Provider performs evil operation with Good's Secret ID on behalf of Evil.

Evil could benefit by:

• exfiltrating Good's Secret via reflection.
• reading or mutating Good's resources accessible via *Good's Secret.

Impact

This requires a complex setup.

Not all shared secrets are used like above, so an actual exploit requires a very specific relation interface, specific semantics of the data in the databag, and an administrator having a reasonable need to deploy two apps (one evil, one good) related to the same (third) provider app.

If exploited, it can be very hard to determine what went wrong after the fact.

Suggested remediation

1. Longer, random secret IDs

For example, if the secret id was extended with a 128-bit nonce, guessing a sibling secret ID would be infeasible, and an attack of this style would require another weakness (e.g. secret IDs exposed in logs)

2. Grantee secret API

Today, an app is not allowed to call secret-info-get on the granted secret. Additionally, granted secrets are not included in the secret-ids output.

Suppose that the Provider could run these hook tools:

The Provider would then able to validate the secret ID it's about to use against:

• the relation in which the secret ID has been passed (good relation 12 or evil relation 14)
• the application or unit name of the secret owner (good or evil)