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The hidden danger of forgetting to specify %SystemRoot% in a custom environment block

When spawning a process using CreateProcess and friends, the child process usually inherits the environment (i.e. all environment variables) of the spawning process. Of course, this behavior can be overridden by creating a custom environment block and passing it to the lpEnvironment parameter of CreateProcess. While the MSDN documentation on CreateProcess does contain a remark saying that current directory information (=C: and friends) should be included in such a custom environment block, it does not mention the importance of SystemRoot.

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