It rather involved being on the other side of this airtight hatchway: Denial of service by high CPU usage

Raymond Chen


We received the following security vulnerability report:

Windows is vulnerable to a denial of service attack that consumes
100% CPU.

  1. Use the following procedure to create a file
    that is enchanted by magic pixie dust:

  2. Rename the file to TEST.EXE.
  3. Execute as many copies of the program as you have CPU cores.

Observe that CPU usage climbs to 100% and never goes down.
This a clear demonstration that Windows is vulnerable to
a denial of service attack from magic pixie dust.

The magic pixie dust is a red herring.
This vulnerability report is basically saying
“If you are allowed to run arbitrary programs,
then it is possible to run a program that
consumes all the available CPU.”

Well, duh.

This is another case of

if I can run an arbitrary program, then I can do arbitrary things
also known as

MS07-052: Code execution results in code execution

in the lingo of Internet memes
“High CPU is high.”)

Now, of course, if the magic pixie dust somehow allows a user
to do things like access resources they do not have access to,
or to circumvent resource usage quotas,
then there would be a serious
problem here,
and if if the high CPU usage could be triggered remotely,
then there is a potential for a denial-of-service attack.
But there was nothing of the sort.
Here’s a much less complicated version of magic pixie dust:

int __cdecl main(int, char **) { for (;;) { } /*NOTREACHED*/ }


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