I. BACKGROUND

Internet Explorer is a graphical web browser developed by Microsoft
Corp. that has been included with Microsoft Windows since 1995. For
more information about Internet Explorer, please the visit following
website: http://www.microsoft.com/ie/

II. DESCRIPTION

Remote exploitation of a stack buffer overflow vulnerability while
handling specific HTML tags in Microsoft Corp.'s Internet Explorer web
browser allows attackers to execute arbitrary code within the context
of the affected user.

On Internet Explorer 5.01 a function return address can be overwritten
with attacker controlled data which results in an exploitable
condition. However on Internet Explorer 6 the vulnerability will only
overflow one byte. For Internet Explorer 6 on Windows 2000 platform,
the overflowed byte is in a local variable, and overwriting it doesn't
affect program execution at all. For Internet Explorer 6 on Windows XP
SP2, the overflowed byte is in the stack cookie, which causes Internet
Explorer to terminate and only results in a denial of service.

III. ANALYSIS

Successful exploitation of this vulnerability would allow an attacker to
execute arbitrary code in the context of the user running the Internet
Explorer. However, the execution of arbitrary code is only possible on
Windows 2000 SP4 running Internet Explorer 5.01.

Exploitation would require an attacker to persuade a user to visit a
malicious website using Internet Explorer.

IV. DETECTION

As of September 2008, iDefense confirms that Internet Explorer 5.01 on
Windows 2000 SP4, is vulnerable. It also causes denial of service for
Internet Explorer 6 on Windows XP SP2. Internet Explorer 7 is not
affected.

V. WORKAROUND

iDefense is not aware of any effective workaround for this issue.
Customers are encouraged to upgrade Internet Explorer to version 6 or
above.

VI. VENDOR RESPONSE

Microsoft has released a patch which addresses this issue. For more
information, consult their advisory at the following URL.

http://www.microsoft.com/technet/security/bulletin/ms08-073.mspx

Microsoft recommends that customers apply the update immediately.

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CVE-2008-4261 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

08/26/2008  Initial Vendor Notification
08/26/2008  Initial Vendor Reply
09/24/2008  Additional Vendor Feedback
12/02/2008  Additional Vendor Feedback
12/09/2008  Coordinated Public Disclosure

IX. CREDIT

This vulnerability was discovered by Jun Mao of iDefense Labs.

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Aviso original:
http://labs.idefense.com/intelligence/vulnerabilities/