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Vulnerability in Microsoft Excel Allows Code Execution (MS07-044)
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SUMMARY
A remote code execution vulnerability exists in the way Excel handles
malformed Excel files. An attacker could exploit the vulnerability by
sending a malformed file which could be included as an e-mail attachment,
or hosted on a malicious or compromised Web site.
DETAILS
Affected Software:
*
<http://www.microsoft.com/downloads/details.aspx?FamilyId=082B98F7-9556-4F1F-823A-C41DDF5A7C9A> Microsoft Office 2000 Service Pack 3
*
<http://www.microsoft.com/downloads/details.aspx?FamilyId=91308769-2577-4F9F-8209-06F2C8C8A86F> Microsoft Office XP Service Pack 3
*
<http://www.microsoft.com/downloads/details.aspx?FamilyId=B0130E9E-8845-4D79-AAA1-A21CC9388ABE> Microsoft Office 2003 Service Pack 2
* <http://www.microsoft.com/mac/downloads.aspx#Office2004> Microsoft
Office 2004 for Mac
CVE Information:
<http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2007-3890>
CVE-2007-3890
Mitigating Factors for Workspace Memory Corruption Vulnerability:
Mitigation refers to a setting, common configuration, or general
best-practice, existing in a default state, that could reduce the severity
of exploitation of a vulnerability. The following mitigating factors may
be helpful in your situation:
* In a Web-based attack scenario, an attacker could host a Web site that
contains a Web page that is used to exploit this vulnerability. In
addition, compromised Web sites and Web sites that accept or host
user-provided content or advertisements could contain specially crafted
content that could exploit this vulnerability. In all cases, however, an
attacker would have no way to force users to visit these Web sites.
Instead, an attacker would have to persuade users to visit the Web site,
typically by getting them to click a link in an e-mail message or Instant
Messenger message that takes users to the attacker's Web site.
* An attacker who successfully exploited this vulnerability could gain
the same user rights as the local user. Users whose accounts are
configured to have fewer user rights on the system could be less impacted
than users who operate with administrative user rights.
* The vulnerability cannot be exploited automatically through e-mail. For
an attack to be successful a user must open an attachment that is sent in
an e-mail message.
* Users who have installed and are using the Office Document Open
Confirmation Tool for Office 2000 will be prompted with Open, Save, or
Cancel before opening a document. The features of the Office Document Open
Confirmation Tool are incorporated in Office XP and later editions of
Office.
Workarounds for Workspace Memory Corruption Vulnerability:
Workaround refers to a setting or configuration change that does not
correct the underlying vulnerability but would help block known attack
vectors before you apply the update. Microsoft has tested the following
workarounds and states in the discussion whether a workaround reduces
functionality:
* Use Microsoft Office File Block policy to block the opening of Office
2003 and earlier documents from unknown or un-trusted sources and
locations.
The following registry scripts can be used to set the File Block policy.
Note Modifying the Registry incorrectly can cause serious problems that
may require you to reinstall your operating system. Microsoft cannot
guarantee that problems resulting from incorrect modification of the
Registry can be solved. Modify the Registry at your own risk.
For Office 2003
Windows Registry Editor Version 5.00
[HKEY_CURRENT_USER\Software\Microsoft\Office\11.0\Excel\Security\FileOpenBlock]
"BinaryFiles"=dword:00000001.
Note In order to use 'FileOpenBlock' with Office 2003, all of the latest
Office 2003 security updates as of May 2007 must be applied.
Impact of Workaround: Users who have configured the File Block policy and
have not configured a special exempt directory as discussed in
<http://support.microsoft.com/kb/922848> Microsoft Knowledge Base Article
92248 will be unable to open Office 2003 files or earlier versions in
Office 2003 or 2007 Microsoft Office System.
* Do not open or save Microsoft Office files that you receive from
untrusted sources or that you receive unexpectedly from trusted sources.
This vulnerability could be exploited when a user opens a specially
crafted file.
FAQ for Workspace Memory Corruption Vulnerability:
What is the scope of the vulnerability?
This is a remote code execution vulnerability. An attacker who
successfully exploited this vulnerability could take complete control of
an affected system remotely. An attacker could then install programs or
view, change, or delete data; or create new accounts with full user
rights.
What causes the vulnerability?
Excel does not perform sufficient validation when denoting the index value
for a Workspace.
What might an attacker use the vulnerability to do?
An attacker who successfully exploited this vulnerability could run
arbitrary code as the logged on user. If a user is logged on with
administrative user rights, an attacker could take complete control of the
affected system. An attacker could then install programs; view, change, or
delete data; or create new accounts with full user rights. Users whose
accounts are configured to have fewer user rights on the system could be
less impacted than users who operate with administrative user rights.
How could an attacker exploit the vulnerability?
This vulnerability requires that a user open a specially crafted Excel
file with an affected version of Microsoft Excel.
In an e-mail attack scenario, an attacker could exploit the vulnerability
by sending a specially-crafted Excel file to the user and by convincing
the user to open the file.
In a Web-based attack scenario, an attacker would have to host a Web site
that contains an Excel file that is used to attempt to exploit this
vulnerability. In addition, compromised Web sites and Web sites that
accept or host user-provided content could contain specially crafted
content that could exploit this vulnerability. An attacker would have no
way to force users to visit a specially crafted Web site. Instead, an
attacker would have to persuade them to visit the Web site, typically by
getting them to click a link that takes them to the attacker's site.
What systems are primarily at risk from the vulnerability?
Systems where Microsoft Excel is used are primarily at risk. Servers could
be at more risk if administrators allow users to log on to servers and to
run programs. However, best practices strongly discourage allowing this.
What does the update do?
The update removes the vulnerability by modifying the way that Microsoft
Excel validates the index value attributes associated with a Workspace.
When this security bulletin was issued, had this vulnerability been
publicly disclosed?
No. Microsoft received information about this vulnerability through
responsible disclosure. Microsoft had not received any information to
indicate that this vulnerability had been publicly disclosed when this
security bulletin was originally issued. This security bulletin addresses
the privately disclosed vulnerability as well as additional issues
discovered through internal investigations.
When this security bulletin was issued, had Microsoft received any reports
that this vulnerability was being exploited?
No. Microsoft had not received any information to indicate that this
vulnerability had been publicly used to attack customers and had not seen
any examples of proof of concept code published when this security
bulletin was originally issued.
ADDITIONAL INFORMATION
The information has been provided by Microsoft Security Bulletin MS07-044.
The original article can be found at:
<http://www.microsoft.com/technet/security/Bulletin/ms07-044.mspx>
http://www.microsoft.com/technet/security/Bulletin/ms07-044.mspx
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