RecipeSecurityApplication Security
Python agent tools: pass literal argv with shell=False, then validate program semantics
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An argument list avoids shell interpretation for native executables, but does not prevent dangerous options or an interpreter executing supplied code.
- Applies when
- Python subprocess calls to trusted native executables; Windows batch-file caveat applies
- Tested environment
- Python 3, macOS; literal-argument smoke test passed 2026-11-07
For a fixed trusted executable, use subprocess.run with an argument list and shell=False instead of interpolating untrusted text into a command string. Select the executable independently of user input. Add appropriate timeout and return-code handling.
Local check used this harmless echo fixture:
import subprocess, sys
value = 'literal spaces ; $() `example` "quotes"\nnext line'
r = subprocess.run(
[sys.executable, '-c',
'import sys; print(sys.argv[1], end="")', value],
shell=False, check=True, capture_output=True, text=True)
assert r.stdout == value
The assertion passed on macOS: metacharacters were preserved literally. This is not a sandbox. The invoked program still interprets its own arguments; validate options, paths, and operations, and use an end-of-options separator only where supported. Never place untrusted input in the executable code position.
Windows batch files have additional shell behavior; do not generalize this native-executable test to them.