Vulnerability Note VU#683612

Microsoft Hyperlink Object Library buffer overflow

Microsoft's bulletin states that the following Windows operating systems are affected by this vulnerability:

• Microsoft Windows 2000 Service Pack 4
• Microsoft Windows XP Service Pack 1 and Service Pack 2
• Microsoft Windows XP Professional x64 Edition
• Microsoft Windows Server 2003 and Service Pack 1
• Microsoft Windows Server 2003 for Itanium-based Systems and Service Pack 1
• Microsoft Windows Server 2003 x64 Edition

Microsoft has released updates in Microsoft Security Bulletin MS06-050 to addess this issue.

Workarounds

Microsoft lists the following workarounds for this vulnerability.

Modify the Access Control List to deny access to Hlink.dll for all users

Disabling the Hlink.dll registry key can protect the affected system from attempts to exploit this vulnerability. By disabling the Hlink.dll registry key, hyperlinks embedded in Microsoft Office documents cannot be edited or opened.

Click Start, click Run, and type cacls %windir%\system32\hlink.dll /d everyone, and click ok

Modify the Access Control List to disable the HLINK registry key

Modifying the HLINK registry key in the Windows registry will help prevent the exploitation of this vulnerability. By modifying the HLINK registry key, hyperlinks embedded in Microsoft Office documents cannot be edited or opened.

Please see the Microsoft Security Bulletin MS06-050 for further details and cautions regarding use of the Registry Editor.

For Windows 2000
1. Click Start, click Run, and type regedit32, click OK
2. Expand HKEY_CLASSES_ROOT, expand CLSID, and click 79eac9d0-baf9-11ce-8c82-00aa004ba90b
3. Click Security, and then click Permissions
4. Uncheck the Allow Inheritable Permissions from the parent to propagate to this object check box. If asked to select from Copy, Remove, or Cancel; select Remove and then click OK.
5. An alert will be displayed that no one will be able to access this registry key. Click Yes.

For Windows XP Service Pack 1 or Later
1. Click Start, click Run, and type regedit, click OK
2. Expand HKEY_CLASSES_ROOT, expand CLSID, and click 79eac9d0-baf9-11ce-8c82-00aa004ba90b
3. Click Security, and then click Permissions
4. Click Advanced
5. Uncheck the Inherit from parent the permission entried that apply to child objects. Include these with entries explicitly defined here. check box. If asked to select from Copy, Remove, or Cancel; select Remove and then click OK.
6. An alert will be displayed that no one will be able to access this registry key. Click Yes, and then click OK to close the Permissions for 79eac9d0-baf9-11ce-8c82-00aa004ba90b dialog box.

Read e-mail messages in plain text

Open only hyperlinks in Microsoft Office documents that come from trusted sources.

http://www.microsoft.com/technet/security/bulletin/ms06-050.mspx

Credit

Thanks to Microsoft Security for reporting this vulnerability in Microsoft Security Bulletin MS06-050. Microsoft, in turn, thanks Steve Tai of CSC Australia Pty Limited for reporting the vulnerability to them.

This document was written by Katie Washok.

Other Information

If you have feedback, comments, or additional information about this vulnerability, please send us email.