Public Vulnerability Reports

Microsoft Internet Explorer HTML Tag Long File Name Extension Stack Buffer Overflow Vulnerability



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:


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.


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.


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.


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


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

Microsoft recommends that customers apply the update immediately.


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 (, which standardizes names for security problems.


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


This vulnerability was discovered by Jun Mao of iDefense Labs.

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