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OSSN/OSSN-0008

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Revision as of 04:13, 8 March 2014 by Nkinder (talk | contribs) (→‎Recommended Actions)

DoS style attack on noVNC server can lead to service interruption or disruption

Summary

There is currently no limit on the number of noVNC or SPICE console sessions that can be established against a single user token. This enables launching a Denial of Service (DoS) style attack by establishing many console sessions against a single virtual machine instance through the console proxy. This can cause instance access timeouts and general service response degradation on the console host.

Affected Services / Software

Horizon (VNC Console through browser), Nova (noVNC proxy), 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:

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

Contacts / References

Retrieved from "https://wiki.openstack.org/w/index.php?title=OSSN/OSSN-0008&oldid=45043"