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[OpenStack Infra <1939733@xxxxxxxxxxxxxxxxxx>]

Reviewed:  https://review.opendev.org/c/openstack/ossa/+/806754
Committed: https://opendev.org/openstack/ossa/commit/55e0ee4953446267d7900bda9cdfdc9f44a6b72d
Submitter: "Zuul (22348)"
Branch:    master

commit 55e0ee4953446267d7900bda9cdfdc9f44a6b72d
Author: Jeremy Stanley <fungi@xxxxxxxxxxx>
Date:   Tue Aug 31 13:56:02 2021 +0000

    Add OSSA-2021-005 (CVE-2021-40085)
    
    Change-Id: I58b8c608547e24ee144cab805d17c55045e4279a
    Closes-Bug: #1939733


** Changed in: ossa
       Status: In Progress => Fix Released

** CVE added: https://cve.mitre.org/cgi-bin/cvename.cgi?name=2021-40085

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https://bugs.launchpad.net/bugs/1939733

Title:
  [OSSA-2021-005] Arbitrary dnsmasq reconfiguration via extra_dhcp_opts
  (CVE-2021-40085)

Status in neutron:
  In Progress
Status in OpenStack Security Advisory:
  Fix Released

Bug description:
  Application doesnt check the input values for extra_dhcp_opts port
  parameter allowing user to use a newline character. The values from
  extra_dhcp_opts are used in rendering of opts file which is passed to
  dnsmasq as a dhcp-optsfile. Considering this, an attacker can inject
  any options to that file.

  The main direct impact in my opinion is that attacker can push
  arbitrary dhcp options to another instances connected to the same
  network. And due to we are able to modify our own port connected to
  external network, it is possible to push dhcp options to the instances
  of another tennants using the same external network.

  If we go further, there is an known buffer overflow vulnerability in
  dnsmasq
  (https://thekelleys.org.uk/gitweb/?p=dnsmasq.git;a=commitdiff;h=7d04e17444793a840f98a0283968b96502b112dc)
  which was not considered as a security issue due to attacker cannot
  control dhcp opts in most cases and therefore this vulnerability is
  still exists in most distributives (e.g Ubuntu 20.04.1). In our case
  dhcp opts is exactly what attacker can modify, so we can trigger
  buffer overflow there. I even managed to write an exploit which lead
  to a remote code execution using this buffer overflow vulnerability.

  Here the payload to crash dnsmasq as a proof of concept:
  ```
  PUT /v2.0/ports/9db67e0f-537c-494a-a655-c8a0c518d57e HTTP/1.1
  Host: openstack
  X-Auth-Token: TOKEN
  Content-Type: application/json
  Content-Length: 170

  {"port":{
  "extra_dhcp_opts":[{"opt_name":"zzz",
  "opt_value":"xxx\n128,aa:bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb\n120,aa.cc\n128,:"
  }]}}
  ```

  Tested on ocata, train and victoria versions.

  Vulnerability was found by Pavel Toporkov

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