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Replace unsafe `pyyaml` loader with `SafeLoader`

pixee:python/harden-pyyaml​

ImportanceReview GuidanceRequires Scanning Tool
MediumMerge Without ReviewNo

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](https://github.com/yaml/pyyaml/wiki/PyYAML-yaml.load(input\)-Deprecation) 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)

If you have feedback on this codemod, please let us know!

F.A.Q.​

Why is this codemod marked as Merge Without Review?​

This codemod replaces any unsafe loaders with the SafeLoader, which is already the recommended replacement suggested in yaml documentation. We believe this replacement is safe and should not result in any issues.

Codemod Settings​

N/A

References​