TANDBERG Video Communication Server Static SSH Host Keys

                   Virtual Security Research, LLC.
                         Security Advisory


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/


Product Description
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
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
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
The TANDBERG VCS appliance is deployed by default with a DSA ssh key pair stored in files:

In tested versions of the firmware, this default key has a fingerprint of: 

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
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
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.

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:

Common Vulnerabilities and Exposures (CVE) Information
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.

Thanks to TANDBERG for the quick initial response and cooperation.



1. TANDBERG - Video Communication Server

2. TANDBERG VCS Firmware Downloads

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

To view the advisory as a txt. click here.

Editor’s note: This work was originally published by VSR on their website at https://www.vsecurity.com/resources/advisories.htmlVSR is now a part of NCC Group, so we have migrated this content to research.nccgroup.com. The advisory text as above has been copy-pasted to this blog for historical reference.

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