Python possesses many mechanisms to invoke an external executable. If the desired executable path is not fully qualified relative to the filesystem root then this may present a potential security risk.

In POSIX environments, the PATH environment variable is used to specify a set of standard locations that will be searched for the first matching named executable. While convenient, this behavior may allow a malicious actor to exert control over a system. If they are able to adjust the contents of the PATH variable, or manipulate the file system, then a bogus executable may be discovered in place of the desired one. This executable will be invoked with the user privileges of the Python process that spawned it, potentially a highly privileged user.

This test will scan the parameters of all configured Python methods, looking for paths that do not start at the filesystem root, that is, do not have a leading ‘/’ character.

Bad practice

import subprocess

subprocess.run(['calculator', '-u', 'critical', msg], check=True) # Sensitive, Path not qualified from root

Recommended

import subprocess

subprocess.run(['/usr/bin/calculator', '-u', 'critical', msg], check=True) # Path qualified from root

References:

Bandit B607
OWASP Top 10 2021 Category A03 - Injection

Zxce3 / userbot

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