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Glance configuration option can lead to privilege escalation


Glance exposes a configuration option called `use_user_token` in the configuration file `glance-api.conf`. It should be noted that the default setting (`True`) is secure. If, however, the setting is changed to `False` and valid admin credentials are supplied in the following section (`admin_user` and `admin_password`), Glance API commands will be executed with admin privileges regardless of the intended privilege level of the calling user.

Affected Services / Software

Glance, Juno, Kilo, Liberty


The `use_user_token` configuration option was created to enable automatic re-authentication for tokens whch are close to expiration, thus preventing the tokens from expiring in the middle of longer-lasting Glance commands. Unfortunately the implementation enables privilege escalation attacks by automatically executing API commands as an administrator level user.

By default `use_user_token` is set to `True` which is secure. If the option is disabled (set to `False`) and valid admin credentials are specified in the `glance-api.conf` file, API commands will be executed as the supplied admin user regardless of the intended privileges of the calling user. Glance API v2 configurations which don't enable the registry service (`data_api = glance.db.registry.api`) aren't affected.

Enabling unauthenticated and lower privileged users to execute Glance commands with administrator privileges is very dangerous and may expose risks including:

  • tampering with images
  • deleting images
  • denial of service attacks

Recommended Actions

A comprehensive fix will be included in the Mitaka release. Meanwhile it is recommended that all users ensure that `use_user_token` is left at the default setting (`True`) or commented out.

Contacts / References