Opera Software Opera Web Browser URL Parsing Heap Overflow Vulnerability

iDefense Security Advisory 10.17.06
http://www.idefense.com/intelligence/vulnerabilities/
Oct 17, 2006

I. BACKGROUND

Opera is a cross-platform web browser. More information is available
from http://www.opera.com/

II. DESCRIPTION

Remote exploitation of a heap overflow vulnerability within version 9 of
Opera Software's Opera Web browser could allow an attacker to execute
arbitrary code on the affected host.

A flaw exists within Opera when parsing a tag that contains a URL. A
heap buffer with a constant size of 256 bytes is allocated to store the
URL, and the tag's URL is copied into this buffer without sufficient
bounds checking of its length. The vulnerable code would look something
like this in C/C++:

char *local_url = malloc(256);

strcpy(local_url, tag_url);

This URL can be inserted into any tag, such as an iframe.  The range of
characters that can be used to overflow the buffer is limited.

III. ANALYSIS

Successful remote exploitation allows an attacker to execute arbitrary
code with the privileges of the logged in user.  A failed exploitation
attempt may result in the browser crashing.  The attacker would first
need to construct a website containing the malicious tag and trick the
vulnerable user into visiting the site. This would trigger the
vulnerability and allow the code to execute with the privileges of the
local user.

The range of characters available does not make this vulnerability
significantly more difficult to exploit.  Through the use of JavaScript
or large compressed image files the attacker can have nearly complete
control of the heap.

IV. DETECTION

iDefense Labs has confirmed Opera versions 9.0 and 9.01 on both Windows
and Linux are vulnerable. Version 8 is not vulnerable.

V. WORKAROUND

iDefense is currently unaware of any effective workarounds for this
vulnerability.

VI. VENDOR RESPONSE

Opera has addressed this vulnerability with version 9.02 of the Opera
Web Browser.  More information can be found in Opera's advisory at
http://www.opera.com/support/search/supsearch.dml?index=848.

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CVE-2006-4819 to this issue. This is a candidate for inclusion in
the CVE list (http://cve.mitre.org), which standardizes names for
security problems.

VIII. DISCLOSURE TIMELINE

09/15/2006  Initial vendor notification
09/29/2006  Initial vendor response
10/17/2006  Coordinated public disclosure

IX. CREDIT

The discoverer of this vulnerability wishes to remain anonymous.

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X. LEGAL NOTICES

Copyright © 2006 iDefense, Inc.

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Disclaimer: The information in the advisory is believed to be accurate
at the time of publishing based on currently available information. Use
of the information constitutes acceptance for use in an AS IS condition.
There are no warranties with regard to this information. Neither the
author nor the publisher accepts any liability for any direct, indirect,
or consequential loss or damage arising from use of, or reliance on,
this information.