Peter Winter-Smith of NGSSoftware has discovered a high risk vulnerability
in the Lexmark Printer Sharing service which could allow a remote,
unauthenticated attacker to execute arbitrary code on a Lexmark printer
user's computer system with Local System privileges.

There is no known official patch or workaround for this issue, as Lexmark
have proven unresponsive throughout the investigation and have failed
to provide us with a response to our queries on many occasions.

Communications between NGS and Lexmark to date are summed up in the
following time-line:

[28/09/2005] Initial email to support@lexmark.com
[28/09/2005] Automated reply from support@lexmark.com
[29/09/2005] Re-sent email to csupportuk@lexmark.co.uk .. No response
[03/10/2005] Mass mail to secure@lexmark.com, security@lexmark.com,
             security-alert@lexmark.com, info@lexmark.com .. No response
[04/10/2005] First response from Lexmark's 'Task ID IE THIRD LEVEL
             ESCALATIONS' thanking NGS for the email dated the 28th Sept.
             asking for further details.
[04/10/2005] Details of the vulnerability provided to Lexmark .. No response
[11/10/2005] Follow-up email to Lexmark .. No response
[18/10/2005] Follow-up email to Lexmark .. No response
[24/10/2005] Follow-up email to Lexmark .. No response
[08/11/2005] Follow-up email to Lexmark .. No response
[30/12/2005] Follow-up email to Lexmark .. No response
[07/01/2006] Informing Lexmark of this advisory .. No response

>From our tests it seems that the following workaround will prevent the
vulnerability from being present by removing the vulnerable service so that
it cannot start. This should not prevent the printer from working in normal
operations, however if a user is depending on the Lexmark Printer Sharing
services for network printing this workaround may impact that level of
functionality.

NGS do not take any responsibility for the following information being
correct or for any of the results which may occur as a result of taking the
following actions.

Workaround:

1. Launch the Services console by taking the following actions:
 - Click the 'Start' menu.
 - Select 'Run'.
  - In the 'Run' command text area type 'services.msc' and click 'Ok'.
2. Find and right click the 'LexBce Server' entry. From the right click menu
   select the 'Stop' item. Confirm that you wish to stop the service and all
   dependencies.
3. Open the '%systemroot%\system32' folder by taking the following actions:
  - Click the 'Start' menu.
  - Select 'Run'.
  - In the 'Run' command text area type '%systemroot%\system32' and click
    'Ok'.
4. Locate the file named 'LexPPS.EXE'. Right click this file and select
   'Rename'. Enter a new name for the file, I recommend 'LexPPS.EXE.vuln'.
5. In the Services console, locate and right click the 'LexBce Server' and
   select 'Start'.
6. In the Services console, locate and right click the 'Print Spooler' and
   select 'Start'.

This disclosure was made in accordance with the NGS responsible disclosure
policy which can be viewed online at:

http://www.ngssoftware.com/disclosure.pdf

NGSSoftware will withhold technical details of this flaw for at least one
month. Full technical details will be published on or after the 7th March
2006.

NGSSoftware Insight Security Research
http://www.ngssoftware.com
http://www.databasesecurity.com/
http://www.nextgenss.com/
+44(0)208 401 0070