OSSN/OSSN-0008

Summary
There is currently no limit to the number of noVNC or SPICE console sessions that can be established by a single user. The console host has limited resources and an attacker launching many sessions may be able to exhaust the available resources, resulting in a Denial of Service (DoS) condition.

Affected Services / Software
Horizon, Nova ,noVNC proxy, SPICE console, Grizzly, Havana

Discussion
Currently with a single user token, no restrictions are enforced on the number or frequency of noVNC or SPICE console sessions that may be established. While a user can only access their own virtual machine instances, resources can be exhausted on the console proxy host by creating an excessive number of simultaneous console sessions. This can result in timeouts for subsequent connection requests to instances using the same console proxy. Not only would this prevent the user from accessing their own instances, but other legitimate users would also be deprived of console access. Further, other services running on the noVNC proxy and Compute hosts may degrade in responsiveness.

By taking advantage of this lack of restrictions around noVNC or SPICE console connections, a single user could cause the console proxy endpoint to become unresponsive, resulting in a Denial Of Service (DoS) style attack. It should be noted that there is no amplification effect.

Recommended Actions
For current stable OpenStack releases (Grizzly, Havana), users need to workaround this vulnerability by using rate-limiting proxies to cover access to the noVNC proxy service. Rate-limiting is a common mechanism to prevent DoS and Brute-Force attacks.

For example, if you are using a proxy such as Repose, enable the rate limiting feature by following these steps:


 * https://repose.atlassian.net/wiki/display/REPOSE/Rate+Limiting+Filter

Future OpenStack releases are looking to add the ability to restrict noVNC and SPICE console connections.

Contacts / References

 * Author: Sriram Subramanian, CloudDon
 * Author: Nathan Kinder, Red Hat
 * This OSSN : https://bugs.launchpad.net/ossn/+bug/1227575
 * Original LaunchPad Bug : https://bugs.launchpad.net/nova/+bug/1227575
 * OpenStack Security ML : openstack-security@lists.openstack.org
 * OpenStack Security Group : https://launchpad.net/~openstack-ossg