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Credit:
The information has been provided by Microsoft Product Security.
The original article can be found at: http://www.microsoft.com/technet/security/bulletin/MS08-015.mspx
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Affected Software
Office Suite and Other Software - Component - Maximum Security Impact - Aggregate Severity Rating - Bulletins Replaced by This Update
* Microsoft Office 2000 Service Pack 3 - Outlook 2000 Service Pack 3 (KB946986) - Remote Code Execution - Critical - MS07-003
* Microsoft Office XP Service Pack 3 - Outlook 2002 Service Pack 3 (KB946985) - Remote Code Execution - Critical - MS07-003
* Microsoft Office 2003 Service Pack 2 - Outlook 2003 Service Pack 2 (KB945432) - Remote Code Execution - Critical - MS07-003
* Microsoft Office 2003 Service Pack 3 - Outlook 2003 Service Pack 3 (KB945432) - Remote Code Execution - Critical - None
* 2007 Microsoft Office System - Outlook 2007 (KB946983) - Remote Code Execution - Critical - None
Non-Affected Software:
Office Suite and Other Software
* 2007 Microsoft Office System Service Pack 1
* Outlook 2007 Service Pack 1
Outlook URI Vulnerability - CVE-2008-0110
A remote code execution exists in Outlook. The vulnerability could allow remote code execution if Outlook is passed a specially crafted mailto URI. 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.
CVE Information:
CVE-2008-0110
Mitigating Factors for Outlook URI Vulnerability - CVE-2008-0110
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 would have to host a Web site and convince a user to click on a specially crafted mailto URI in order to 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 convince 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.
* The vulnerability cannot be exploited automatically through e-mail. For an attack to be successful, a user must open an e-mail message that contains a specially crafted mailto URI and click on the mailto link.
* This vulnerability is not exploitable by simply viewing an e-mail through the Outlook preview pane.
Workarounds for Outlook URI Vulnerability - CVE-2008-0110
Disable the Outlook mailto handler
Disabling the mailto handler in the system registry key helps protect affected systems from attempts to exploit this vulnerability.
Note: Using Registry Editor incorrectly can cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk. For information about how to edit the registry, view the "Changing Keys And Values" Help topic in Registry Editor (Regedit.exe) or view the "Add and Delete Information in the Registry" and "Edit Registry Data" Help topics in Regedt32.exe.
Perform the following steps:
1. Click Start, click Run, type regedit and then click OK.
2. Expand HKEY_CLASSES_ROOT.
3. Expand mailto.
4. To backup the registry before your edit it, left-click on File menu, select Export... In the Export Registry File dialog box, type mailto_backup.reg and select Save.
5. Right-click on "mailto" and select Delete.
Impact of Workaround: Users who have configured their systems with this workaround will be unable to process mailto requests that would normally launch any application s mailto action.
How to Undo the Workaround:
1. Click Start, click Run, type regedit and then click OK.
2. Expand HKEY_CLASSES_ROOT.
3. Expand mailto.
4. To restore the registry, left-click on File menu, select Import... In the Import Registry File dialog box, select mailto_backup.reg and select Open.
FAQ for Outlook URI Vulnerability - CVE-2008-0110
What is the scope of the vulnerability?
This is a remote code execution vulnerability in Outlook. An attacker who successfully exploited this vulnerability could take complete control of an affected system.
What causes the vulnerability?
Microsoft Outlook does not perform sufficient validation of mailto URIs passed to the Outlook client.
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 an affected Microsoft Outlook system be passed a specially crafted mailto URI.
In a Web-based attack scenario, an attacker would have to host a Web site and convince a user to click on a specially crafted mailto URI in order to 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 convince 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 such as desktop clients or terminal server systems where Microsoft Outlook is used are primarily at risk.
What does the update do?
The update removes the vulnerability by modifying the way that the Microsoft Outlook client validates the mailto URIs passed to it.
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.
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