CVE-2020-14343 is a critical-severity (CVSS 9.8) Improper Input Validation vulnerability in pyyaml. 1 public exploit reference exists, so weaponization risk is real. A fix is available for pyyaml — see the affected versions and patch details below.
Improper Input Validation in PyYAML
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2020-14343 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 385,738 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
pyyamlReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
A vulnerability was discovered in the PyYAML library in versions before 5.4, 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. This flaw allows an attacker to execute arbitrary code on the system by abusing the python/object/new constructor. This flaw is due to an incomplete fix for CVE-2020-1747.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | pyyaml | all versions | 5.4pip install --upgrade 'pyyaml==5.4' |
Affected Products
communications cloud native core network function cloud native environmentoraclepyyamlpyyamlResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for pyyaml, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update pyyaml to 5.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-14343 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
This CVE has already been fixed in RHEL-9 with initial release of PyYaml v5.4-1. Ansible Tower 3.7 uses affected version of PyYAML 3.12 from RHEL, but the use of load() is specified with a SafeLoader when it is called. So Ansible Tower and Ansible Engine are not affected. Red Hat Quay, from version 3.4 uses the…
Use `yaml.safe_load` or the SafeLoader loader when you parse untrusted input.Source: Red Hat security advisory for CVE-2020-14343 (CC BY 4.0)
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat Enterprise Linux 8 | python38:3.8-8040020210420090415.6dfe838a | RHSA-2021:2583 |
| Red Hat Satellite 6.10 for RHEL 7 | python-pyyaml-0:5.4.1-1.el7pc | RHSA-2021:4702 |
Frequently Asked Questions
Is CVE-2020-14343 in your dependencies?
Find it across PyPI, including transitive dependencies.