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Microsoft Excel Filter Record Code Execution Vulnerability
iDefense Security Advisory 05.08.07
http://labs.idefense.com/intelligence/vulnerabilities/ May 08, 2007
I. BACKGROUND Microsoft Excel is the spreadsheet application from the Microsoft Office System. More information is available at the following URL.
II. DESCRIPTION Remote exploitation of an input validation error in the handling of AutoFilter records in Excel BIFF8 format spreadsheet files by Microsoft Corp.'s Excel 2003 could allow an attacker to execute arbitrary code in the context of the current user.
The AutoFilter feature of Excel allows data not matching a specified criteria to be filtered out. By creating a document containing a specially crafted filter record, an attacker is able to cause an invalid memory access leading to arbitrary code execution.
III. ANALYSIS Exploitation allows attackers to execute arbitrary code in the context of the user who started Excel.
Exploitation requires that attackers social engineer users into opening a maliciously crafted file in Excel. Reliable exploitation appears to require knowledge of the specific version of Excel being used. Likely attack vectors include sending the file as an e-mail attachment or linking to the file on a website.
By default systems with Office 2000 installed open Office documents, including Excel spreadsheet files, from websites without prompting the user, which allows attackers to exploit this vulnerability without user interaction. Later versions of Office do not open these documents automatically unless the user has chosen this behavior.
Enabling hardware DEP (data execution prevention) on systems that support it (i.e., Windows XP SP2 and Windows Server 2003 on hardware with AMD processors that support NX or Intel processors supporting XD) mitigates this vulnerability. The hardware DEP feature prevents code from being executed from areas of memory that do not have the 'executable' bit set. While it may be possible for attackers to bypass this restriction, it can prevent some typical exploitation methods.
IV. DETECTION iDefense has confirmed Microsoft Excel 2003 is vulnerable. Previous versions are also likely to be affected. Excel 2007 does not appear to be vulnerable.
V. WORKAROUND iDefense is currently unaware of an effective workarounds for this issue.
VI. VENDOR RESPONSE Microsoft has addressed this vulnerability within MS07-023. For more information, consult their bulletin at the following URL.
VII. CVE INFORMATION The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2007-1214 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 02/08/2007 Initial vendor notification 02/08/2007 Initial vendor response 05/08/2007 Coordinated public disclosure
IX. CREDIT This vulnerability was discovered by Greg MacManus (iDefense Labs).
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X. LEGAL NOTICES Copyright © 2007 iDefense, Inc.
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