Remote Assistance and the Secure Desktop

When a User consents to having a Helper share control of her computer during a Remote Assistance session, the User has the option of allowing the Helper to respond to UAC prompts (Figure 22-1) Typically, UAC prompts appear on the Secure Desktop (which is not remoted), and consequently the Helper cannot see or respond to Secure Desktop prompts. The Secure Desktop mode is the same mode that a user sees when she logs on to her computer or presses the Secure Attention Sequence (SAS) keystroke (Ctrl+Alt+Delete). UAC elevation prompts are displayed on the Secure Desktop instead of the user's normal desktop to protect the user from unknowingly allowing malware to run with elevated privileges on her computer. The User must provide consent to a UAC prompt to return to her normal desktop and continue working. This consent requires either clicking Continue (if the user is a local administrator on her computer) or by entering local administrative credentials (if she is a standard user on her computer)

FIGURE 22-1 The User has the option of allowing the Helper to respond to UAC prompts when the Remote Assistance session is in the Control Sharing state .

It is important to understand that the Secure Desktop on the User's computer is not remoted to the Helper's computer. In other words, the Helper can respond only to UAC prompts on the User's computer using the User's own credentials. This means that if the User is a standard user on her computer and the Helper is a local administrator on the User's computer, the Helper can have only administrative privileges on the User's computer if the User can first supply those credentials

Enforcing this limitation is essential to ensure the security of Windows 7 desktops . The reason behind this design decision is that, if Remote Assistance was architected to allow the Helper to remotely elevate the User's privileges, the User would be able to terminate the Remote Assistance session and thus steal local administrative credentials from the Helper.

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