MS15-074: Vulnerability in Windows Installer service could allow elevation of privilege: July 14, 2015

Important

• All future security and nonsecurity updates for Windows RT 8.1, Windows 8.1, and Windows Server 2012 R2 require update 2919355 to be installed. We recommend that you install update 2919355 on your Windows RT 8.1-based, Windows 8.1-based, or Windows Server 2012 R2-based computer so that you receive future updates.
• If you install a language pack after you install this update, you must reinstall this update. Therefore, we recommend that you install any language packs that you require before you install this update. For more information, see Add language packs to Windows.

Information for installations that are dependent on the less-secure behavior

ImportantFollow the steps in this section carefully. Serious problems might occur if you modify the registry incorrectly. Before you modify it, back up the registry for restoration in case problems occur.

• Applications that use installations that are dependent on the less-secure behavior may not install correctly. If it is critical that installation for these applications be enabled, IT administrators can temporarily opt-out of this security fix by changing a registry setting.
  
  Note Be aware that this opt-out method disables this security fix.
  
  To temporarily undo the security fix in KB 3072630, follow these steps:
  
  1. Click Start, click Run, type regedit in the Open box, and then click OK.
  2. Locate and then click the following subkey in the registry:
     
     HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\Installer
     Note If this subkey does not exist, create it.
  3. On the Edit menu, point to New, and then click DWORD Value.
  4. For the DWORD name, type RemappedElevatedProxiesPolicy, and then press Enter.
  5. Right-click RemappedElevatedProxiesPolicy, and then click Modify.
  6. In the Value data box, type 1, and then click OK.
  7. Install the required application.
  8. After the application installs successfully, reset the RemappedElevatedProxiesPolicy DWORD value to 0 to re-enable the security fix for KB 3072630.

After you install this security update, the behavior of custom actions for accessing user hives in the registry will have changed. This security update more strictly enforces the requirement that only custom actions that use impersonation can access HKCU for the current user.

The following is the new behavior:

• Custom actions with impersonation can access HKCU for the current user.
• Custom action that run as System will access HKCU for System instead of HKCU for the current user.

After you install this security update, if you find that some registry keys in HKCU are no longer set by custom actions, you may have to re-design the MSI package so that this custom action is impersonated.

Known issues in this security update

• 3153727 Windows Installer with certain actions can't be installed on Windows Server 2012 R2 or Windows Server 2008 R2 SP1