Asterisk Project Security Advisory - AST-2008-006

   +------------------------------------------------------------------------+
   |      Product       | Asterisk                                          |
   |--------------------+---------------------------------------------------|
   |      Summary       | 3-way handshake in IAX2 incomplete                |
   |--------------------+---------------------------------------------------|
   | Nature of Advisory | Remote amplification attack                       |
   |--------------------+---------------------------------------------------|
   |   Susceptibility   | Remote unauthenticated sessions                   |
   |--------------------+---------------------------------------------------|
   |      Severity      | Critical                                          |
   |--------------------+---------------------------------------------------|
   |   Exploits Known   | Yes                                               |
   |--------------------+---------------------------------------------------|
   |    Reported On     | April 18, 2008                                    |
   |--------------------+---------------------------------------------------|
   |    Reported By     | Joel R. Voss aka. Javantea < jvoss AT altsci DOT  |
   |                    | com >                                             |
   |--------------------+---------------------------------------------------|
   |     Posted On      | April 22, 2008                                    |
   |--------------------+---------------------------------------------------|
   |  Last Updated On   | April 22, 2008                                    |
   |--------------------+---------------------------------------------------|
   |  Advisory Contact  | Tilghman Lesher < tlesher AT digium DOT com >     |
   |--------------------+---------------------------------------------------|
   |      CVE Name      | CVE-2008-1897                                     |
   +------------------------------------------------------------------------+

   +------------------------------------------------------------------------+
   | Description | Javantea originally reported an issue in IAX2, whereby   |
   |             | an attacker could send a spoofed IAX2 NEW message, and   |
   |             | Asterisk would start sending early audio to the target   |
   |             | address, without ever receiving an initial response.     |
   |             | That original vulnerability was addressed in June 2007,  |
   |             | by requiring a response to the initial NEW message       |
   |             | before starting to send any audio.                       |
   |             |                                                          |
   |             | Javantea subsequently found that we were doing           |
   |             | insufficent verification of the ACK response and that    |
   |             | the ACK response could be spoofed, just like the initial |
   |             | NEW message. We have addressed this failure with two     |
   |             | changes. First, we have started to require that the ACK  |
   |             | response contains the unique source call number that we  |
   |             | send in our reply to the NEW message. Any ACK response   |
   |             | that does not contain the source call number that we     |
   |             | have created will be silently thrown away. Second, we    |
   |             | have made the generation of our source call number a     |
   |             | little more difficult to predict, by randomly selecting  |
   |             | a source call number, instead of allocating them         |
   |             | sequentially.                                            |
   +------------------------------------------------------------------------+

   +------------------------------------------------------------------------+
   | Workaround | Disable remote unauthenticated IAX2 sessions, by          |
   |            | disallowing guest access.                                 |
   +------------------------------------------------------------------------+

   +------------------------------------------------------------------------+
   | Resolution | Upgrade your Asterisk installation to revision 114561 or  |
   |            | later, or install one of the releases shown below.        |
   +------------------------------------------------------------------------+

   +------------------------------------------------------------------------+
   | Commentary | We would like to thank Javantea for notifying us of this  |
   |            | problem; however, we note that he posted exploit code     |
   |            | prior to that notification, which is considered           |
   |            | irresponsible behavior in the whitehat security industry. |
   |            | In the future, advance notice of any such release would   |
   |            | be appreciated.                                           |
   +------------------------------------------------------------------------+

   +------------------------------------------------------------------------+
   |                           Affected Versions                            |
   |------------------------------------------------------------------------|
   |            Product            |  Release   |                           |
   |                               |   Series   |                           |
   |-------------------------------+------------+---------------------------|
   |     Asterisk Open Source      |   1.0.x    | All versions              |
   |-------------------------------+------------+---------------------------|
   |     Asterisk Open Source      |   1.2.x    | All versions prior to     |
   |                               |            | 1.2.28                    |
   |-------------------------------+------------+---------------------------|
   |     Asterisk Open Source      |   1.4.x    | All versions prior to     |
   |                               |            | 1.4.20                    |
   |-------------------------------+------------+---------------------------|
   |   Asterisk Business Edition   |   A.x.x    | All versions              |
   |-------------------------------+------------+---------------------------|
   |   Asterisk Business Edition   |   B.x.x    | All versions prior to     |
   |                               |            | B.2.5.2                   |
   |-------------------------------+------------+---------------------------|
   |   Asterisk Business Edition   |   C.x.x    | All versions prior to     |
   |                               |            | C.1.8.1                   |
   |-------------------------------+------------+---------------------------|
   |          AsteriskNOW          |   1.0.x    | All versions prior to     |
   |                               |            | 1.0.3                     |
   |-------------------------------+------------+---------------------------|
   | Asterisk Appliance Developer  |   0.x.x    | All versions              |
   |              Kit              |            |                           |
   |-------------------------------+------------+---------------------------|
   |  s800i (Asterisk Appliance)   |   1.0.x    | All versions prior to     |
   |                               |            | 1.1.0.3                   |
   +------------------------------------------------------------------------+

   +------------------------------------------------------------------------+
   |                              Corrected In                              |
   |------------------------------------------------------------------------|
   |                   Product                   |         Release          |
   |---------------------------------------------+--------------------------|
   |            Asterisk Open Source             |          1.2.28          |
   |---------------------------------------------+--------------------------|
   |            Asterisk Open Source             |          1.4.20          |
   |---------------------------------------------+--------------------------|
   |          Asterisk Business Edition          |         B.2.5.2          |
   |---------------------------------------------+--------------------------|
   |          Asterisk Business Edition          |         C.1.8.1          |
   |---------------------------------------------+--------------------------|
   |                 AsteriskNOW                 |          1.0.3           |
   |---------------------------------------------+--------------------------|
   |         s800i (Asterisk Appliance)          |         1.1.0.3          |
   +------------------------------------------------------------------------+

   +------------------------------------------------------------------------+
   |   Links    | https://www.altsci.com/concepts/page.php?s=asteri&p=2     |
   +------------------------------------------------------------------------+

   +------------------------------------------------------------------------+
   | Asterisk Project Security Advisories are posted at                     |
   | http://www.asterisk.org/security                                       |
   |                                                                        |
   | This document may be superseded by later versions; if so, the latest   |
   | version will be posted at                                              |
   | http://downloads.digium.com/pub/security/AST-2008-006.pdf and          |
   | http://downloads.digium.com/pub/security/AST-2008-006.html             |
   +------------------------------------------------------------------------+

   +------------------------------------------------------------------------+
   |                            Revision History                            |
   |------------------------------------------------------------------------|
   |        Date         |        Editor        |      Revisions Made       |
   |---------------------+----------------------+---------------------------|
   | April 22, 2008      | Tilghman Lesher      | Initial release           |
   +------------------------------------------------------------------------+

               Asterisk Project Security Advisory - AST-2008-006
              Copyright (c) 2008 Digium, Inc. All Rights Reserved.
  Permission is hereby granted to distribute and publish this advisory in its
                           original, unaltered form.