Product

Asterisk

Summary

Traffic amplification in IAX2 firmware provisioning system

Nature of Advisory

Traffic amplification attack

Susceptibility

Remote unauthenticated sessions

Severity

Critical

Exploits Known

No

Reported On

July 18, 2008

Reported By

Tilghman Lesher < tlesher AT digium DOT com >

Posted On

July 22, 2008

Last Updated On

December 12, 2008

Advisory Contact

Tilghman Lesher < tlesher AT digium DOT com >

CVE Name

CVE-2008-3264

Description

An attacker may request an Asterisk server to send part of a firmware image. However, as this firmware download protocol does not initiate a handshake, the source address may be spoofed. Therefore, an IAX2 FWDOWNL request for a firmware file may consume as little as 40 bytes, yet produces a 1040 byte response. Coupled with multiple geographically diverse Asterisk servers, an attacker may flood an victim site with unwanted firmware packets.

Workaround

The only device which used this firmware upgrade procedure was the IAXy ATA device, and the last firmware upgrade was more than 18 months ago. It is unlikely that any IAXy devices in use today still need the last firmware upgrade. Therefore, deleting the firmware image from the directory where it is served from and sending a reload event to the Asterisk server is sufficient to purge the firmware image from the Asterisk server's memory. An Asterisk server which is unable to serve out the requested firmware image will reply to any such request with a much smaller REJECT packet, which is smaller than even the FWDOWNL packet.

Resolution

This firmware download procedure has been disabled by default in Asterisk. If you should still need to upgrade IAXys in the field, there is an option 'allowfwdownload' which can be enabled. However, due to the reasons specified on the Workaround section, it is recommended that you leave this option disabled and enable it only on secure internal networks when an IAXy is initially provisioned.

Affected Versions

Product

Release Series

Asterisk Open Source

1.0.x

All versions

Asterisk Open Source

1.2.x

All versions prior to 1.2.30

Asterisk Open Source

1.4.x

All versions prior to 1.4.21.2

Asterisk Addons

1.2.x

Not affected

Asterisk Addons

1.4.x

Not affected

Asterisk Business Edition

A.x.x

All versions

Asterisk Business Edition

B.x.x

All versions prior to B.2.5.4

Asterisk Business Edition

C.x.x

All versions prior to C.1.10.3

AsteriskNOW

pre-release

All versions

Asterisk Appliance Developer Kit

0.x.x

All versions

s800i (Asterisk Appliance)

1.0.x

All versions prior to 1.2.0.1

Corrected In

Product

Release

Asterisk Open Source

1.2.30

Asterisk Open Source

1.4.21.2

Asterisk Business Edition

B.2.5.4

Asterisk Business Edition

C.1.10.3

Asterisk Business Edition

C.2.0.3

s800i (Asterisk Appliance)

1.2.0.1

Patches

URL

Version

http://downloads.digium.com/pub/security/AST-2008-011-1.2.patch

1.2

http://downloads.digium.com/pub/security/AST-2008-011-1.4.patch

1.4

Links

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-2008-011.pdf and http://downloads.digium.com/pub/security/AST-2008-011.html

Revision History

Date

Editor

Revisions Made

July 22, 2008

Tilghman Lesher

Initial release

July 22, 2008

Tilghman Lesher

Revised C.1 version numbers

December 12, 2008

Tilghman Lesher

Added patches