[Full-disclosure] Authentication Bypass of Snom Phone Web Interface

["Walter Sprenger" <walter.sprenger@xxxxxxx>]

#############################################################
#
# COMPASS SECURITY ADVISORY
# http://www.csnc.ch/en/downloads/advisories.html
#
#############################################################
#
# Product:   Snom VoIP/SIP Phones (Snom300, Snom320, Snom360, 
#            Snom370, Snom820)
# Vendor:    snom technology AG
# CVD ID:    CVE-2009-1048
# Subject:   Authentication Bypass of Snom Phone Web Interface
# Risk:      High
# Effect:    Remote
# Author:    Walter Sprenger
# Date:      August 13, 2009
#
#############################################################

Introduction:
-------------
The VoIP phones of snom technology AG can be configured, monitored
or controlled with a browser connecting to the built in web interface.
It is strongly recommended to enable authentication on the web
interface and to set a strong password. 
By constructing a specially crafted HTTP request the authentication 
of the web interface can be completely bypassed.

Impact:
-------
Access to the web interface without authentication enables a
malicious user to [2]:
- call expensive numbers
- listen to the phone conversation by capturing the network traffic
- read SIP username and password
- read and modify all configuration parameters of the phone
- redirect phone calls to another VoIP server
- activate the microphone and listen to the conversation in the room

Affected:
---------
- The tests have been conducted on a Snom360, Firmware versions: 
  - snom360 linux 3.25/snom360-SIP 6.5.17
  - snom360 linux 3.25/snom360-SIP 6.5.18
  - snom360-SIP 7.1.30
  - snom360-SIP 7.1.35 14552
- All Snom300, Snom320, Snom360, Snom370 and Snom820 with firmware 
  versions below 6.5.20, 7.1.39 and 7.3.14 are vulnerable according 
  to snom technology AG
- Not vulnerable: 
  - Firmware version 6.5.20 and higher
  - Firmware version 7.1.39 and higher
  - Firmware version 7.3.14 and higher


Technical Description:
----------------------
The web interface of the Snom VoIP/SIP phones is protected by 
Basic Authentication or Digest Authentication.
The authentication can be completely bypassed by modifying the 
HTTP request. A normal browser sets the request header "Host:" 
to the IP address or the host name that is entered in the URL 
field of the browser. If the request header is modified to 
contain the value "Host: 127.0.0.1", all pages and functions 
of the web interface can be reached without prompting the user 
to authenticate.

How to test:
------------
curl -H "Host: 127.0.0.1" http://<IP address of phone>/
curl -k -H "Host: 127.0.0.1" https://<IP address of phone>/

-> if the phone is vulnerable, the index page of the web 
   interface is returned
-> if the phone is not vulnerable, an 
   "HTTP/1.1 401 Unauthorized" response is returned


Workaround / Fix:
-----------------
- Upgrade to firmware version 6.5.20, 7.1.39, 7.3.14 or above
- Disable the web interface until a firmware upgrade is installed


Timeline:
---------
Vendor Notified: March 19, 2009
Vendor Status:   Replied on March 19 and March 30, vulnerability 
                 confirmed      
Vendor Response: Problem fixed in firmware version 7.1.39/7.3.14. 
                     Problem will be fixed in version 6.
Patch available: Firmware upgrade to versions 6.5.20, 7.1.39, 7.3.14 
                 and above      

References:
-----------
[1]: http://www.snom.de
[2]:
http://www.csnc.ch/misc/files/publications/V6_attacking_voip_v1.0.pdf

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