Replace unsafe `pyyaml` loader with `SafeLoader`

The default loaders in PyYAML are not safe to use with untrusted data. They potentially make your application vulnerable to arbitrary code execution attacks. If you open a YAML file from an untrusted source, and the file is loaded with the default loader, an attacker could execute arbitrary code on your machine.

This codemod hardens all yaml.load() calls against such attacks by replacing the default loader with yaml.SafeLoader. This is the recommended loader for loading untrusted data. For most use cases it functions as a drop-in replacement for the default loader.

Calling yaml.load() without an explicit loader argument is equivalent to calling it with Loader=yaml.Loader, which is unsafe. This usage has been deprecated since PyYAML 5.1. This codemod will add an explicit SafeLoader argument to all yaml.load() calls that don't use an explicit loader.

The changes from this codemod look like the following:

  import yaml
  data = b'!!python/object/apply:subprocess.Popen \\n- ls'
- deserialized_data = yaml.load(data, yaml.Loader)
+ deserialized_data = yaml.load(data, Loader=yaml.SafeLoader)

unitedstates / congress-legislators

Replace unsafe `pyyaml` loader with `SafeLoader` #922