Software Engineering Institute

The Microsoft Windows "MHTML" protocol handler contains an information disclosure vulnerability in the way that it interprets HTTP headers. The "MHTML" protocol handler fails to properly interpret HTTP headers when returning MHTML content, which may allow Internet Explorer to bypass Internet Explorer domain restrictions.

By convincing a user to visit a specially crafted website, a remote, unauthenticated attacker may be able to access sensitive information.

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This issue is addressed by Microsoft Security Bulletin MS07-034.

Workarounds

Microsoft has provided the following workarounds to address this issue:

Disable the MHTML protocol handler.

1. Click Start and then click Run. Enter regedit.exe in the text box and click OK.
2. Navigate to HKEY_CLASSES_ROOT\CLSID\{05300401-BCBC-11d0-85E3-00C04FD85AB4}.
3. Right click {05300401-BCBC-11d0-85E3-00C04FD85AB4} and select Permissions.
4. Click Advanced.
5. Uncheck Allow inheritable permissions from the parent to propagate…
6. Click Remove, and then click OK. Click Yes and OKon subsequent screens.
Impact of workaround: This workaround disables page rendering for MHTML Web pages.


Configure Internet Explorer to prompt before running Active Scripting or to disable Active Scripting in the Internet and Local intranet security zone.

1. In Internet Explorer, click Internet Options on the Tools menu.
2. Click the Security tab.
3. Click Internet, and then click Custom Level.
4. Under Settings, in the Scripting section, under Active Scripting, click Prompt or Disable, and then click OK.
5. Click Local intranet, and then click Custom Level.
6. Under Settings, in the Scripting section, under Active Scripting, click Prompt or Disable, and then click OK.
7. Click OK two times to return to Internet Explorer.

Please see Microsoft Security Bulletin MS07-034 for further details.