OSSN-0076: Glance Image service v1 and v2 api image-create vulnerability

Summary

No limits are enforced within the Glance image service for both v1 and v2 /images API POST method for authenticated users, resulting in possible denial of service attacks through database table saturation.

Affected Services / Software

All versions of Glance image service.

Discussion

Within the Glance image service, calls to the POST method within v1 or v2/images creates an image (record) in queued status. There is no limit enforced within the Glance API on the number of images a single tenant may create, just on the total amount of storage a single user may consume.

Therefore a user could either maliciously or unintentionally fill multiple database tables (images, image_properties, image_tags, image_members) with useless image records, thereby causing a denial of service by lengthening transaction response times in the Glance database.

Recommended Actions

For all versions of Glance that expose either the v1 and v2/images API, operators are recommended to deploy external rate-limiting proxies or web application firewalls, to provide a front layer of protection to glance. The Glance database should be monitored for abnormal growth. Although rate-limiting does not eliminate this attack vector, it will slow it to the point where you can react prior to a denial of service occurring.

The following solutions may be considered, however it is key that the operator carefully plans and considers the individual performance needs of users and services within their OpenStack cloud, when configuring any rate limiting functionality.

Repose

Repose provides a rate limiting filter, that can utilise limits by IP, Role (OpenStack Identity v3 filter) or header. https://repose.atlassian.net/wiki/display/REPOSE/Rate+Limiting+Filter

NGINX

NGINX provides the limit_req_module, which can be used to provide a global rate limit. By means of a map, it can be limited to just the POST method. http://nginx.org/en/docs/http/ngx_http_limit_req_module.html

HAProxy

HAProxy can provide inherent rate-limiting using stick-tables with a General Purpose Counter (gpc). http://blog.haproxy.com/2012/02/27/use-a-load-balancer-as-a-first-row-of-defense-against-ddos

Apache

A number of solutions can be explored here as follows.

• mod_ratelimit: http://httpd.apache.org/docs/2.4/mod/mod_ratelimit.html

• mod_qos: http://opensource.adnovum.ch/mod_qos/dos.html

• mod_evasive: https://www.digitalocean.com/community/tutorials/how-to-protect-against-dos-and-ddos-with-mod_evasive-for-apache-on-centos-7

• mod_security: https://www.modsecurity.org/

Limit add_image to admin role

Another possible mitigation is to restrict image creation to the admin role, however this should only be done for those cases in which there are Glance nodes dedicated to end-user access only. Restriction to admin only on Glance nodes that serve OpenStack services will for example, remove the ability to create snapshots from the Compute API or to create bootable volumes from Cinder.

To restrict image creation to the role admin only, amend /etc/glance/policy.json accordingly:

"add_image": "role:admin",

Contacts / References

Author: Luke Hinds, Red Hat

• This OSSN : https://docs.openstack.org/security-notes/OSSN-0076.html

• Original LaunchPad Bug : https://bugs.launchpad.net/ossn/+bug/1545092

• OpenStack Security ML : openstack-security@lists.openstack.org

• OpenStack Security Group : https://launchpad.net/~openstack-ossg