Thanks Nathan, good to publish!

-----Original Message-----
From: "Nathan Kinder" <email address hidden>
Sent: ‎3/‎7/‎2014 8:33 PM
To: "<email address hidden>" <email address hidden>
Subject: [Openstack-security] [Bug 1227575] Re: DoS style attack on noVNCserver can lead to service interruption or disruption

Here's an updated OSSN draft that covers all of the issues mentioned in
my previous comment (in the appropriate e-mail format).  I also removed
the reference to rate-limiting in the Security Guide, as it doesn't
actually contain any information on how to do rate limiting.  It only
mentioned that QOSaaS plans to offer rate limiting, which isn't
applicable here.

If this looks fine to everyone else, I'll go ahead and publish it.

-----------------------------------------------------------------------------------------
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, 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 ###
This OSSN : https://wiki.openstack.org/wiki/OSSN/OSSN-0008
Original LaunchPad Bug : https://bugs.launchpad.net/nova/+bug/1227575
OpenStack Security ML : <email address hidden>
OpenStack Security Group : https://launchpad.net/~openstack-ossg

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https://bugs.launchpad.net/bugs/1227575

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

Status in OpenStack Compute (Nova):
  In Progress
Status in OpenStack Security Notes:
  New

Bug description:
  There is no limiting on the number of VNC sessions that can be created for a single user's VNC token.
  Any attempt to create multiple (say hundreds or thousands) of websocket connections to the VNC server
  results in many connection timeouts. Due to these connection timeout error, other users trying to access their 
  VM's VNC console cannot do so.

  A sample script that tries to create 100,000 connections to Nova noVNC proxy, shows timeout errors
  Script: http://paste.openstack.org/show/47254/

  Script output.... connections get timed out after a while
  -------------------
  ....
  ..

  Creating Connection
  Receiving...
  Received 'RFB 003.008
  '
  Creating Connection
  Receiving...
  Received 'RFB 003.008
  '
  Creating Connection
  Receiving...
  Received 'RFB 003.008
  '
  Creating Connection
  Receiving...
  Received 'RFB 003.008
  '
  Creating Connection
  Receiving...
  Received 'RFB 003.008
  '
  Creating Connection
  Receiving...
  Received 'RFB 003.008
  '
  Creating Connection
  Receiving...
  timed out
  Creating Connection
  Receiving...
  timed out
  Creating Connection
  Receiving...
  timed out
  Creating Connection
  Receiving...
  timed out
  Creating Connection
  Receiving...
  timed out
  --------------------

  Impact:
  1. Many of the sessions timeout. Any attempt to open other sessions also intermittently fail.
  This can cause serious problems to users already having a running VNC session or trying to create new sessions.

  2. The overall performance and response times of other nova services running on the novnc host, using tcp protocol
  also gets affected after the connection timeout errors.

  For example:
  Before running the sumulate thousands of connections program:
  $ time nova get-vnc-console c1b093a3-f53b-4282-b89c-e68f0fa1b6e5  novnc
  +-------+---------------------------------------------------------------------------------+
  | Type  | Url                                                                             |
  +-------+---------------------------------------------------------------------------------+
  | novnc | http://10.2.3.102:6080/vnc_auto.html?token=e776dd33-422f-4b56-9f98-e317410d0212 |
  +-------+---------------------------------------------------------------------------------+

  real    0m0.751s
  user    0m0.376s
  sys     0m0.084s

  rohit@precise-dev-102:~/tools/websocket-client-0.7.0$

  After running the program, the response time is quite high:
  $ time nova get-vnc-console c1b093a3-f53b-4282-b89c-e68f0fa1b6e5  novnc

  +-------+---------------------------------------------------------------------------------+
  | Type  | Url                                                                             |
  +-------+---------------------------------------------------------------------------------+
  | novnc | http://10.2.3.102:6080/vnc_auto.html?token=6865d675-d852-478b-b1ee-457b092f11b9 |
  +-------+---------------------------------------------------------------------------------+

  real    3m9.231s
  user    0m0.424s
  sys     0m0.108s

  
  Possible solutions:
  1. Allow just 1 session per instance, and raise a new exception, say, VNCSessionAlreadyExists to reject multiple
  connections for the same token, and return an error code to the user.
  2. Make the number of sessions allowed per instance configurable, limited by some count of sessions.

  However, both of these solutions may need to override and modify the do_proxy() method of websockify's WebSocketProxy class, 
  which can lead to maintenance issues.

  Another possible solution would be to implement some kind of callback function in websockify, to which we can pass the token
  for reconnection. This would first need contribution to the websockify project code, and then update Nova.

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