What’s Vulnerable › Vulnerabilities

CVE-2020-1747: Improper Input Validation in PyYAML

• Severity: critical (CVSS 9.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 5.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2020-03-24 · updated 2026-06-17
• Weakness: CWE-20

Description

A vulnerability was discovered in the PyYAML library in versions before 5.3.1, where it is susceptible to arbitrary code execution when it processes untrusted YAML files through the full_load method or with the FullLoader loader. Applications that use the library to process untrusted input may be vulnerable to this flaw. An attacker could use this flaw to execute arbitrary code on the system by abusing the python/object/new constructor.

Affected products

• Fedoraproject Fedora: 30, 31, 32, 33
• openSUSE Leap: 15.1
• Oracle Communications Cloud Native Core Network Function Cloud Native Environment: 22.1.0
• Pyyaml: from 5.1 before 5.3.1 — fixed in 5.3.1
• Pypi Pyyaml: from 5.1 before 5.3.1; 5.1, 5.1.1, 5.1.2, 5.2b1, 5.2, 5.3b1 (+1) — fixed in 5.3.1

How to fix

Upgrade to a fixed version: Pyyaml 5.3.1; Pypi Pyyaml 5.3.1. Check the vendor advisory for mitigations.

References

• http://lists.opensuse.org/opensuse-security-announce/2020-04/msg00017.html
• http://lists.opensuse.org/opensuse-security-announce/2020-05/msg00017.html
• https://bugzilla.redhat.com/show_bug.cgi?id=CVE-2020-1747
• https://github.com/yaml/pyyaml/pull/386
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/7PPAS6C4SZRDQLR7C22A5U3QOLXY33JX/
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/K5HEPD7LEVDPCITY5IMDYWXUMX37VFMY/
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/MMQXSZXNJT6ERABJZAAICI3DQSQLCP3D/
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/WORRFHPQVAFKKXXWLSSW6XKUYLWM6CSH/
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ZBJA3SGNJKCAYPSHOHWY3KBCWNM5NYK2/
• https://www.oracle.com/security-alerts/cpujul2022.html
• http://lists.opensuse.org/opensuse-security-announce/2020-04/msg00017.html
• http://lists.opensuse.org/opensuse-security-announce/2020-05/msg00017.html

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