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Public proof of conceptFix available

CVE-2020-14343

A public proof of concept exists; no exploitation attested.

  • Published2021-02-09
  • WeaknessCWE-20

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

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.

Timeline

dates in UTC
  1. 2021-02-0921:15CVE publishedNVD
  2. 2026-10-2319:23First public proof of conceptPoC-in-GitHub

Observed activity

isMalicious corpus · updated 2026-10-23 18:48 UTC
Indicators tagged with this CVE, per day0 indicators over 7 days
Block these indicators
  • Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2020-14343?format=txt
  • CSV export: https://api.ismalicious.com/edl/cve/CVE-2020-14343?format=csv
  • TAXII collection of exploited CVEs
  • The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD
Oracle communications cloud native core network function cloud native environment
BranchAffectedFixed in
1.10= 1.10.0no fix published
22.1= 22.1.0no fix published
Pyyaml
BranchAffectedFixed in
5.x≥ 5.1, < 5.45.4

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Fix

Advisories and patches

Detection

read 2026-10-23 19:23 UTC
Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof-of-concept repositories
4 repositories, unverifiedj4k0m/loader-CVE-2020-14343Kairo-one/CVE-2020-14343-PyYAMLsijie52/yasa-cve-2020-14343saina15/cve-2020-14343-lab
PoC-in-GitHub

Sources

  • NVDCVSS 3.19.8read 2026-10-23
  • NVDCVSS 2.010read 2026-10-23
  • CNAweakness (CWE)CWE-20read 2026-10-23
  • NVDweakness (CWE)CWE-20read 2026-10-23
  • FIRST EPSSEPSS score6.0 %2026-10-22
  • PoC-in-GitHubproof of concept4read 2026-10-23

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Published
2021-02-09
Last Modified
2026-06-17
NVD status
Modified

Frequently asked questions

What is CVE-2020-14343?

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.

Is CVE-2020-14343 actively exploited?

Active exploitation of CVE-2020-14343 has not been confirmed. Its EPSS score was 6.0% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2020-14343?

CVE-2020-14343 has a CVSS v3 base score of 9.8 (CRITICAL severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

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