[EXPL] Multiple Vulnerabilities in CISCO VoIP Phones (Additional details)

From: support@securiteam.com
Date: 05/23/02


From: support@securiteam.com
To: list@securiteam.com
Date: Thu, 23 May 2002 08:59:20 +0200 (CEST)

The following security advisory is sent to the securiteam mailing list, and can be found at the SecuriTeam web site: http://www.securiteam.com
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  Multiple Vulnerabilities in CISCO VoIP Phones (Additional details)
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SUMMARY

The 7900 line of VoIP phones from Cisco contain remote-accessible code
which can be exploited to cause a denial of service, and possibly leak
information; the phones are also weak in ways that facilitate
man-in-the-middle attacks directed at intercepting telephone traffic.
Vulnerable products include CP-7960, CP-7940, and CP-7910 phones.

For ways of protecting yourself from this vulnerability see our previous
article: <http://www.securiteam.com/securitynews/5VP0M0K75S.html>
Multiple Vulnerabilities in Cisco IP Telephones.

DETAILS

Vulnerabilities:
1. The Cisco 7900 series of phones include a built-in web server on port
80. The server provides several pages of debug and status information
about the phone and is presumably intended for diagnostic purposes.
However the pages require no authentication and some are CGI scripts with
exploitable errors. The most glaring of these is the StreamingStatistics
page. Opening http://>/StreamingStatistics?1 will present a page
of debug statistics as intended. Requesting statistics on a non-existent
stream, e.g.
http://>/StreamingStatistics?7 will return a page
indicating the error. However, requesting statistics for a stream with
sufficiently high ID will cause a hard-reset of the phone.

Testing has produced varying results, but hard reset tends to occur with
IDs > 32768, and using an (arbitrarily selected) ID of 120000 consistently
produces the reset. This results in a reboot process of approximately
15-30 seconds during which the phone is not in service. The result is a
very simple and not at all packet intensive DoS possibility. The attack is
further facilitated the phone's willingness to provide its IP and phone
number through the web page, allowing an attacker to walk a subnet looking
for the correct IP, when targeting a specific extension.

2. Related to #1, another script on the phone's website, PortInformation
has similar, though less catastrophic input validation problems. It uses
the same format as above,
http://>/PortInformation?1 will give
you information on the first Ethernet port of the phone (which has its own
port, as well as a second 10/100 switched port for connecting a computer
to the network without requiring multiple Ethernet drops).

Like StreamingStatistics, PortInformation will indicate an invalid port
number up to a point (again, results vary, but IDs over 32768 seem to
cause the problem consistently). Above that limit, rather than crashing,
the page is generated with what looks like the contents of arbitrary
memory locations. It is conceivable that a dedicated attacker could put
this data to some use. If a tool were developed which could extract from
this, for instance, the phone's recent calls lists, then it would be
possible for an intruder to monitor and map telephone usage within the
system. This is certainly not as dangerous as #1, but it should clearly be
fixed nonetheless.

3. The telephones store all of their network information locally and most
of it is accessible through the "Settings" button on the phone. By
default, these settings are locked (as indicated by a padlock icon when
viewing them) however the key to unlock the settings is the constant
string '**#' (entered from the phone's keypad).

This is not admin-configurable. Once unlocked, several fields can be
specified, including the TFTP server from which the phone receives its
configuration file. Among other things, this file provides the phone with
the list of CallManager IPs who will provide the telephony services. With
one-time physical access to the phone, an attacker could enter an
alternate, malicious TFTP server which would provide the phone with
attacker-controlled CallManager IPs.
In this fashion, the attacker could route all telephone traffic through
his or her systems, presumably recording it or altering it before passing
it to the legitimate CallManager systems for transport. This modification
of the phone's configuration is very unlikely to be noticed, since a user
never has to interact with the network settings menu where these changes
were made.

Vendor Status:
Cisco first contacted March 27, 2002 and responded promptly. They have
releaed an advisory that can be found at:
 <
http://www.securiteam.com/securitynews/5VP0M0K75S.html> Multiple
Vulnerabilities in Cisco IP Telephones.

ADDITIONAL INFORMATION

The information has been provided by <mailto:johnath@johnath.com>
Johnathan Nightingale.

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