I've heard local Windows admins can hijack sessions without passwords. How is this possible? What are the best...
ways to stop this kind of session hijacking?
An attacker with local Windows admin privileges can remotely hijack a user's session without knowing the user's password.
If the targeted user has been locked out of his workstation, the attacker can access it anyway. This action requires the attacker to have the NT AUTHORITY/SYSTEM authority. He can check this out with the whoami command. A Remote Desktop Protocol must be set up to connect to the victim's machine.
Before session hijacking begins, the attacker goes to the Task Manager's Users tab to view the status of each user's account. Using the Task Manager is easier than executing a few command lines to get the status. The local admin's account is always active. Console is assigned as the session name. If, for example, the targeted user is a bank employee who discontinued his session before leaving for lunch, the attacker would be unable to connect to the employee's workstation.
After viewing the Task Manager, the attacker brings up the Command Prompt window. The attacker executes one command line to complete the session hijacking. Arguments (parameters or options) for the PsExec command are changed maliciously. The victim's remote session is connected back to the attacker. The attacker returns to the Task Manager. He maliciously gains access to the victim's session. When the victim returns from lunch, he has no way of knowing he was hijacked.
To stop this type of session hijacking, a group policy should be established. This policy should include preventing an unprivileged user from gaining local admin rights. The policy should also prevent the local admin from returning a user's remote session.
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