Date: 09 August 2007
References: AU-2007.0018 ESB-2007.0576
Click here for printable version
Click here for PGP verifiable version
-----BEGIN PGP SIGNED MESSAGE-----
A U S C E R T A L E R T
AL-2007.0091 -- AUSCERT ALERT
Mozilla Firefox unpatched URI filtering vulnerability allows
9 August 2007
AusCERT Alert Summary
Product: Firefox 220.127.116.11 and prior
Operating System: Windows
Impact: Execute Arbitrary Code/Commands
CVE Names: CVE-2007-4041
Original Bulletin: http://www.kb.cert.org/vuls/id/783400
Comment: This is a newly reported vulnerability distinct from the
URI issue described previously in AusCERT Alert AL-2007.0084.
In this case a user's computer may be remotely compromised when
visiting a malicious web page using Firefox or related browsers on
Windows, if Internet Explorer 7 is also installed on the computer.
This vulnerability remains unfixed in Firefox 18.104.22.168.
Revision History: August 9 2007: Added CVE Name
July 27 2007: Initial Release
- --------------------------BEGIN INCLUDED TEXT--------------------
US-CERT Vulnerability Note VU#783400
Mozilla Firefox URI filtering vulnerability
Mozilla Firefox does not filter input when sending certain URIs to
registered protocol handlers. This may allow a remote, authenticated
attacker to use Firefox as a vector for executing commands on a
A Uniform Resource Identifier (URI) is a string of characters that
can be used to identify a location, resource, or protocol. Mozilla
Firefox passes some URIs to applications that have been registered
to handle them.
Firefox does not filter data passed to certain URIs. An attacker may
be able to construct a malicious URI link that Firefox will pass to
the registered URI handler. Public exploit code exists that uses
mailto, news, nntp, snews, and telnet URI handlers. This public exploit
code appears to rely upon having Internet Explorer 7 installed on a
Microsoft Windows system. Also note that the technique used by the
exploit code may affect applications other than Mozilla Firefox.
A remote, unauthenticated attacker may be able to execute arbitrary
commands, using Firefox as an attack vector.
We are currently unaware of a practical solution to this problem.
Workarounds for users
* Using the about:config interface, setting the
network.protocol-handler.warn-external.snews to true will make
Firefox display a prompt before sending a URI to an external
* Do not click on or follow untrusted links, or links that contain
%00 immediately following the protocol name.
Workarounds for administrators
* Blocking mailto:%00, nntp:%00, news:%00, snews:%00, telnet:%00
strings inside of HTML pages or other network streams using an
application layer firewall or IPS may mitigate this vulnerability.
See the xs-sniper blog for more information about known vulnerable
URIs. Please note that these filters will only work for the public
exploit code that is currently available. Other variations of the
exploit code may be able to bypass these restrictions.
Vendor Status Date Updated
Mozilla Vulnerable 26-Jul-2007
This vulnerability was disclosed by Billy (BK) Rios.
This document was written by Ryan Giobbi.
Date Public 07/25/2007
Date First Published 07/26/2007 04:02:37 PM
Date Last Updated 07/26/2007
Document Revision 17
- --------------------------END INCLUDED TEXT--------------------
You have received this e-mail bulletin as a result of your organisation's
registration with AusCERT. The mailing list you are subscribed to is
maintained within your organisation, so if you do not wish to continue
receiving these bulletins you should contact your local IT manager. If
you do not know who that is, please send an email to firstname.lastname@example.org
and we will forward your request to the appropriate person.
NOTE: Third Party Rights
This security bulletin is provided as a service to AusCERT's members. As
AusCERT did not write the document quoted above, AusCERT has had no control
over its content. The decision to follow or act on information or advice
contained in this security bulletin is the responsibility of each user or
organisation, and should be considered in accordance with your organisation's
site policies and procedures. AusCERT takes no responsibility for consequences
which may arise from following or acting on information or advice contained in
this security bulletin.
NOTE: This is only the original release of the security bulletin. It may
not be updated when updates to the original are made. If downloading at
a later date, it is recommended that the bulletin is retrieved directly
from the author's website to ensure that the information is still current.
Contact information for the authors of the original document is included
in the Security Bulletin above. If you have any questions or need further
information, please contact them directly.
Previous advisories and external security bulletins can be retrieved from:
If you believe that your computer system has been compromised or attacked in
any way, we encourage you to let us know by completing the secure National IT
Incident Reporting Form at:
Australian Computer Emergency Response Team
The University of Queensland
Internet Email: email@example.com
Facsimile: (07) 3365 7031
Telephone: (07) 3365 4417 (International: +61 7 3365 4417)
AusCERT personnel answer during Queensland business hours
which are GMT+10:00 (AEST).
On call after hours for member emergencies only.
-----BEGIN PGP SIGNATURE-----
-----END PGP SIGNATURE-----