Open Stack

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Keystone token scoping provides no security benefit
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### Summary ###
Keystone provides "scoped" tokens that are constrained to use by a
single project. A user may expect that their scoped token can only be
used to perform operations for the project it is scoped to, which is not
the case. A service or other party who obtains the scoped token can use
it to obtain a token for a different authorized scope, which may be
considered a privilege escalation.

### Affected Services / Software ###
Keystone, Diablo, Essex, Folsom, Grizzly, Havana, Icehouse, Juno, Kilo

### Discussion ###
This is not a bug in keystone, it's a design feature that some users may
expect to bring security enhancement when it does not. The OSSG is
issuing this security note to highlight the issue.

Many operations in OpenStack will take a token from the user and pass it
to another service to perform some portion of the intended operation.
This token is very powerful and can be used to perform many actions for
the user. Scoped tokens appear to limit their use to the project and
roles they were granted for but can also be used to request tokens with
other scopes. It's important to note that this only works with currently
valid tokens. Once a token expires it cannot be used to gain a new
token.

Token scoping helps avoid accidental leakage of tokens because using
tokens with other services requires the extra step of requesting a new
re-scoped token from keystone. Scoping can help with audit trails and
promote good code practices. There's currently no way to create a
tightly scoped token that cannot be used to request a re-scoped token. A
scoped token cannot be relied upon to restrict actions to only that
scope.

### Recommended Action ###
Users and deployers of OpenStack must not rely on the scope of tokens
to limit what actions can be performed using them.

Concerned users are encouraged to read (OSSG member) Nathan Kinder's
blog post on this issue and some of the potential future solutions.

### Contacts / References ###
Nathan Kinder on Token Scoping : https://blog-nkinder.rhcloud.com/?p=101
This OSSN : https://wiki.openstack.org/wiki/OSSN/OSSN-0042
Original LaunchPad Bug : https://bugs.launchpad.net/ossn/+bug/1341816
OpenStack Security ML : openstack-security at lists.openstack.org
OpenStack Security Group : https://launchpad.net/~openstack-ossg
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