@stake, Inc.
                              www.atstake.com

                             Security Advisory

Advisory Name: Opera HREF Escaped Server Name Overflow
 Release Date: 10/20/2003
  Application: Opera 7.11, 7.20
     Platform: Windows XP/2000 and GNU/Linux 2.4 tested, others
               may be vulnerable
     Severity: Remote code execution
      Authors: Jesse Burns <jesse@atstake.com>
Vendor Status: Fixed in version 7.21
CVE Candidate: CAN-2003-0870
    Reference: www.atstake.com/research/advisories/2003/a102003-1.txt


Overview:

The Opera browser exhibits a failure when rendering HTML. Certain
HREFs cause a buffer allocated on the heap to overflow. Arbitrary 
bytes in the heap may be overwritten. This can result in the
compromise of systems running Opera. Opera's mail system seems to be
vulnerable also and recovery from reading an email is somewhat
difficult.

An attacker can send an email containing HTML to a user running the
Opera mail client and cause this overflow to occur when the HTML is
rendered. An owner of a web site can craft a malicious web page
containing the problematic HTML to cause an overflow on Opera
clients visiting the site.


Details:

Rendering HREFs with certain illegally escaped server names in the
URL will cause Opera to crash due to a buffer management problem. 
Sometimes the crash is observed immediately, sometimes when the
browser is closed, presumably as the resources are being freed. 

The escaped URLs are of the form:

<a href="file://server%%[many % characters]%%text" ></a> 


Timeline:

09/29/2003 Opera contacted with details of issue
09/30/2003 Vendor responds that they have reproduced problem
10/15/2003 Vendor releases new version of program that includes a
           fix
10/20/2003 Advisory released


Vendor Response:

Opera has release a new version of the software that is available
here:

http://www.opera.com/download/

The change log (http://www.opera.com/windows/changelogs/721/) notes
this fix as:

"Fixed a crash caused by illegally escaped server name"

There is no specific bulletin or warning to users that this release
contains security fixes.


Recommendation:

Upgrade to the 7.21 version of Opera browser for your platform. 

Filter email to remove HTML. Run your web browser and mail client
as a low privileged user.


Common Vulnerabilities and Exposures (CVE) Information:

The Common Vulnerabilities and Exposures (CVE) project has assigned
the following names to these issues.  These are candidates for
inclusion in the CVE list (http://cve.mitre.org), which standardizes
names for security problems.

   CAN-2003-0870 Opera HREF escaped server name overflow


@stake Vulnerability Reporting Policy:
http://www.atstake.com/research/policy/

@stake Advisory Archive:
http://www.atstake.com/research/advisories/

PGP Key:
http://www.atstake.com/research/pgp_key.asc

@stake is currently seeking application security experts to fill
several consulting positions.  Applicants should have strong
application development skills and be able to perform application
security design reviews, code reviews, and application penetration
testing.  Please send resumes to jobs@atstake.com.

Copyright 2003 @stake, Inc. All rights reserved.