Open Stack

Restarting memcached loses revoked token list
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### Summary ###
When a cloud is deployed using Memcache as a backend for Keystone tokens
there is a security concern that restarting Memcached will lose the list
of revoked tokens, potentially allowing bad tokens / users to access the
system after they had been revoked.

### Affected Services / Software ###
Keystone, Memcache

### Discussion ###
There might be ways to mitigate in the future, such as running memcached
on multiple machines to ensure redundancy should the Keystone server
fail. In a clustered environment, it will only be an issue if all of the
memcached machines shutdown.

Memcachedb might also be a potential way to mitigate.
http://memcachedb.org/

NOTE: Some deployments may intentionally flush Memcached in response to
https://bugs.launchpad.net/ossn/+bug/1179955 - please exercise caution
when considering how to approach this problem.

### Recommended Actions ###
This is a fundamental problem with using in-memory ephemeral storage for
security information. If your deployment has strong security
requirements or a reliance on up-to-date revoked token information we
suggest you consider using an on-disk DB such as MySQL / PostgreSQL or
perhaps look into Memcachedb.

### Contacts / References ###
This OSSN : https://bugs.launchpad.net/ossn/+bug/1182920
Blueprint :
https://blueprints.launchpad.net/keystone/+spec/revocation-backend
OpenStack Security ML : openstack-security at lists.openstack.org
OpenStack Security Group : https://launchpad.net/~openstack-ossg



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