DUO109.md

DUO109

This linter searches for insecure use of the yaml module. Its parsing functions dump, dump_all, load, and load_all allow for arbitrary code execution. Thus, they should be avoided in favor of their safe equivalents: safe_dump, safe_dump_all, safe_load, and safe_load_all.

Problematic code

import yaml

malicious_user_input = "your_files: !!python/object/apply:subprocess.check_output ['ls']"
yaml.load(malicious_user_input)

Correct code

import yaml

malicious_user_input = "your_files: !!python/object/apply:subprocess.check_output ['ls']"
yaml.safe_load(malicious_user_input)

Rationale

Arbitrary code execution allows an attacker to perform any action within the context of the system the bug is found. E.g. open a reverse shell to a system of their choosing, install malware by downloading and running a payload, silently log actions performed on the victim system, etc.

Arbitrary code execution bugs are effectively the keys to the castle. We'd like to avoid using the above function because it commonly allows for these types of bugs.

Exceptions

None