CODEWITHSUNDEEP
pythonsubprocess
user3175543
user3175543

Reputation: 121

Python Subprocess Security

I understand why using 'shell=True' can be a security risk if you have untrusted input. However, I don't understand how 'shell=False' avoids the same risks.

Presumably if I wanted to allow a user to provide an input he might input: var="rm -rf /"

My code might simply:

subprocess.call(var,shell=True) # bad stuff

Or I might do:

varParts=var.split()
subprocess.call(varParts,shell=False) # also bad, right?

It would seem that the assumption is one wouldn't go through the trouble of processing the input as I did in the second example and therefore this would/could not happen?

Upvotes: 12

Views: 15278

Answers (1)

unutbu
unutbu

Reputation: 880547

With shell=False, the args[0] is the program to be executed and args[1:] are passed as arguments to this program.

So, for example,

subprocess.call(['cat','nonexistent;','rm','-rf'])

calls the cat program and sends the 3 strings 'nonexistent;','rm','-rf' as arguments to cat. This is perfectly safe, though invalid since -r is an invalid option to cat.

However, arbitrary user input could still be unsafe. If, for example, you were to allow the user to control the program to be called, as in

subprocess.call(['rm','-rf'])

Upvotes: 22

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