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Microsoft Word RTF File Parsing Heap Corruption Vulnerability
iDefense Security Advisory 05.08.07
http://labs.idefense.com/intelligence/vulnerabilities/ May 08, 2007
I. BACKGROUND Microsoft Word is a word processing application from Microsoft Office. Rich Text Format (RTF) is a document file format developed by Microsoft for cross-platform document interchange. For more information about Microsoft Word, see following web site.
II. DESCRIPTION Remote exploitation of a heap corruption vulnerability in Microsoft Corp.'s Word could allow attackers to execute arbitrary code under the privileges of the target user.
This vulnerability specifically exists in the handling of property strings of certain control words in an RTF document. In certain circumstances, these property strings can be written into a memory region which has already been deallocated and heap corruption can occur.
III. ANALYSIS Successful exploitation of this vulnerability allows remote attackers to execute arbitrary code on the affected host within the context of the user who opened the malicious RTF document with Microsoft Word.
Microsoft Word, if installed, will be the default application for opening RTF files. If Microsoft Word is not installed, WordPad will be the default application for opening RTF files, which is not vulnerable to this attack.
Exploitation requires that the user opens a specially crafted RTF document with a vulnerable application. The most likely exploitation vector involves convincing a user to open an RTF document sent to them via e-mail, or linked on a website.
Enabling hardware Data Execution Prevention (DEP) on systems that support it (i.e., Windows XP SP2 and Windows Server 2003 SP1 on hardware with AMD processors supporting NX or Intel processors supporting XD) mitigates this vulnerability. While it may be possible for attackers to bypass this protection, it can prevent some typical exploitation methods.
IV. DETECTION iDefense has confirmed that winword.exe file version 11.0.8106.0, as included with a fully patched Microsoft Word 2003 SP2, is vulnerable. Previous versions of Microsoft Word are also likely to be affected.
V. WORKAROUND Since WordPad.exe is not affected by this vulnerability, changing the default association for RTF files to use WordPad is considered an effective workaround. However, simply changing the file extension can bypass this workaround.
VI. VENDOR RESPONSE Microsoft has addressed this vulnerability within MS07-024. 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-2007-1202 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 02/27/2007 Initial vendor notification 02/27/2007 Initial vendor response 05/08/2007 Coordinated public disclosure
IX. CREDIT This vulnerability was reported to iDefense by an anonymous researcher. Further analysis was performed by Jun Mao (iDefense Labs).
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X. LEGAL NOTICES Copyright © 2007 iDefense, Inc.
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