CVE-2009-4510: TANDBERG VCS Static SSH Host Keys

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               Virtual Security Research, LLC.
                  http://www.vsecurity.com/
                     Security Advisory

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Advisory Name: TANDBERG Video Communication Server Static SSH Host Keys
Release Date: 2010-04-09
Application: Video Communication Server (VCS)
Versions: x4.3.0, x4.2.1, and possibly earlier
Severity: High
Discovered by: Jon Hart
Advisory by: Timothy D. Morgan <tmorgan (a) vsecurity . com>
Vendor Status: Firmware version x5.1.1 released [2].
CVE Candidate: CVE-2009-4510
Reference: http://www.vsecurity.com/resources/advisory/20100409-2/

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Product Description

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• From [1]:

"The Video Communication Server (VCS) is an integral part of the TANDBERG
Total Solution and is the center of the video communications network,
connecting the benefits of video conferencing and telepresence to other
communications environments including unified communications and IP Telephony
networks."

Vulnerability Overview

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On December 2nd, VSR identified a SSH service authentication weakness
vulnerability in the TANDBERG's Video Communication Server. This issue would
allow an attacker with privileged network access to conduct server impersonation
and man-in-the-middle attacks on administrator SSH sessions. Successful attacks
could yield shell access to vulnerable appliances.

Product Background

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The TANDBERG Video Communication Server is a Linux-based appliance which
supports the interoperation of a plethora of video and voice communications
devices. The VCS provides several system shell accounts accessible via the SSH
protocol.

Vulnerability Details

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The TANDBERG VCS appliance is deployed by default with a DSA ssh key pair stored
in files:
/tandberg/sshkeys/ssh_host_dsa_key
/tandberg/sshkeys/ssh_host_dsa_key.pub

In tested versions of the firmware, this default key has a fingerprint of:
49:53:bf:94:2a:d7:0c:3f:48:29:f7:5b:5d:de:89:b8

No new key is generated upon installation. In addition, this default key would
overwrite any SSH server keys, if installed by security-conscious administrators
previously, during a firmware upgrade.

Due to the public nature of this key (see firmware downloads [2]) an attacker
would be able to conduct server impersonation and man-in-the-middle attacks on
SSH connections directed at any TANDBERG VCS device. A successful exploit would
most likely yield an attacker shell access to the device with privileges of the
victim client.

Versions Affected

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VSR has observed this vulnerability in version x4.2.1. Based on preliminary
analysis of configuration files and scripts [2], versions x4.3.0 and x5.0 also
appear to be vulnerable. Earlier versions have not been tested.

Vendor Response

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The following timeline details TANDBERG's response to the reported issue:

2009-12-09 Preliminary notice to TANDBERG. TANDBERG responded immediately.

2009-12-22 VSR provided TANDBERG a draft advisory.

2009-12-28 TANDBERG provided VSR with a beta version of the x5.0 firmware,
but this did not appear to correct the issue.

2010-01-22 TANDBERG provided VSR with a beta version of the x5.1 firmware,
but this did not appear to correct the issue for existing
installations, since old vulnerable keys would be preserved.

2010-01-28 TANDBERG explained that changing SSH keys automatically on
administrators may cause backward compatibility problems.
Therefore, TANDBERG decided to preserve old keys even when
upgrading a system which contains a vulnerable key.
Administrators will instead be warned in the web console that a
vulnerable key is in use and will be expected to update host keys
manually.

2010-03-26 TANDBERG provided VSR with a release candidate firmware for
version x5.1.1.

2010-04-07 TANDBERG VCS firmware version x5.1.1 released [2].

2010-04-09 VSR advisory released.

Recommendation

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Immediately replace the current SSH host key with a new one. This may
be accomplished through one of several methods. One approach is to
simply log in to the device locally and use the ssh-keygen utility to
replace the keys stored in /tandberg/sshkeys/. Consult TANDBERG
documentation for other methods.

After replacing the SSH host keys, it is recommended that the VCS
firmware be upgraded to X5.1.1 as soon as possible. NOTE: Upgrading or
downgrading to versions prior to X5.1.1 will cause any custom SSH host
keys to be overwritten. Version X5.1.1 and later should preserve any
custom host keys previously installed. As a precaution, after upgrading
or downgrading VCS firmwares, verify that the host key has not changed back
to the publicly known one with fingerprint:
49:53:bf:94:2a:d7:0c:3f:48:29:f7:5b:5d:de:89:b8

Common Vulnerabilities and Exposures (CVE) Information

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The Common Vulnerabilities and Exposures (CVE) project has assigned
the number CVE-2009-4510 to this issue. This is a candidates for
inclusion in the CVE list (http://cve.mitre.org), which standardizes
names for security problems.

Acknowledgements

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Thanks to TANDBERG for the quick initial response and cooperation.

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References:

1. TANDBERG - Video Communication Server
   http://www.tandberg.com/video-conferencing-network-infrastructure/video-communication-server.jsp

2. TANDBERG VCS Firmware Downloads
   http://ftp.tandberg.com/pub/software/vcs/

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  Copyright 2009,2010 Virtual Security Research, LLC. All rights reserved.
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