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Discussed in IRC[0] - conclusion is this is a Valid bug but there is no
reasonable attack vector (the data could be used in determining whom to
attempt to gain access to, but does not provide any means of direct
attack). The data is *NOT* intended to be public but is not really
explicitly private/privileged either. The API Contract and current
behavior is an acceptable (as long as it is documented in this bug)
behavior to leave.

This may still warrant an OSSN outlining that the data is available but
there is minimal or no risk.

[0] http://eavesdrop.openstack.org/irclogs/%23openstack-keystone
/%23openstack-keystone.2019-08-16.log.html#t2019-08-16T21:36:28

** Changed in: keystone
       Status: In Progress => Won't Fix

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https://bugs.launchpad.net/bugs/1840288

Title:
  Trusts GET API leaks existence information to unauthorized users

Status in OpenStack Identity (keystone):
  Won't Fix
Status in OpenStack Security Advisory:
  Won't Fix

Bug description:
  The current implementation of the GET /v3/OS-TRUST/trusts/{trust_id}
  API leaks information about the existence of a trust to unauthorized
  users.

  If an authenticated user requests a trust that either does not exist
  or has no remaining uses, the returned response is a 404 regardless of
  whether the user is an admin or a trustor/trustee of the hypothetical
  (e.g. soft-deleted or used-up) trust. If the trust does exist but the
  user has no access to it, the returned response is a 403. If an
  attacker had some reasonable way of guessing or brute-forcing the UUID
  of a trust, they could use this leak to confirm its existence. A valid
  trust ID can then be used as part of a token request in combination
  with the trustee's credentials.

  The issue is here:

  https://opendev.org/openstack/keystone/src/commit/5beddfaddbb4c59d7a24fa1d7ff534da4c69ddc5/keystone/api/trusts.py#L149-L150

  The current "identity:get_trust" default policy rule is "" which is
  all-permissive, and authorization is hardcoded in the trust controller
  code. To enforce the "only the trustor or trustee can GET this" rule,
  it does a lookup of the trust and doesn't catch a NotFound, thereby
  leaking it directly back to the requester.

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