Potential token revocation abuse via group membership
Deletion of groups in Keystone causes token revocation for group members. If group capabilities are delegated to users, they can abuse those capabilities to maliciously revoke tokens for other users.
Affected Services / Software
Keystone, Grizzly, Havana, Icehouse
If a group is deleted from Keystone, all tokens for all users that are members of that group are revoked. By adding users to a group without those users' knowledge and then deleting that group, a group admin can revoke all of the users' tokens. While the default policy file gives the group admin role to global admin, an alternative policy could delegate the create_group, add_user_to_group, and delete_group capabilities to a set of users. In such a system, those users will also get a token revocation capability. Only setups using a custom policy file in Keystone are affected.
Keystone's default policy.json file uses the admin_required rule for the create_group, delete_group, and add_user_to_group capabilities. It is recommended that you use this default configuration if possible. Here is an example snippet of a properly configured policy.json file:
"identity:create_group": "rule:admin_required", "identity:delete_group": "rule:admin_required", "identity:add_user_to_group": "rule:admin_required",
If you need to delegate the above capabilities to non-admin users, you need to take into account that those users will be able to revoke tokens for other users by performing group deletion operations. You should take caution with who you delegate these capabilities to.