AST-2008-006 - 3-way handshake in IAX2 incomplete

           Asterisk Project Security Advisory - AST-2008-006

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| Product | Asterisk |
|--------------------±--------------------------------------------------|
| Summary | 3-way handshake in IAX2 incomplete |
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| Nature of Advisory | Remote amplification attack |
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| Susceptibility | Remote unauthenticated sessions |
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| Severity | Critical |
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| Exploits Known | Yes |
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| Reported On | April 18, 2008 |
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| Reported By | Joel R. Voss aka. Javantea < jvoss AT altsci DOT |
| | com > |
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| Posted On | April 22, 2008 |
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| Last Updated On | April 22, 2008 |
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| Advisory Contact | Tilghman Lesher < tlesher AT digium DOT com > |
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| CVE Name | CVE-2008-1897 |
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| 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. |
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| Workaround | Disable remote unauthenticated IAX2 sessions, by |
| | disallowing guest access. |
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| Resolution | Upgrade your Asterisk installation to revision 114561 or |
| | later, or install one of the releases shown below. |
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| 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. |
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| Links | https://www.altsci.com/concepts/page.php?s=asteri&amp;p=2 |
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| 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 |
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           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.