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No exploitation reportedFix available

CVE-2019-20477

No exploitation reported by the sources we read.

  • Published2020-02-19
  • Fixed in5.2 · 5.2b1
  • WeaknessCWE-502

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

PyYAML 5.1 through 5.1.2 has insufficient restrictions on the load and load_all functions because of a class deserialization issue, e.g., Popen is a class in the subprocess module. NOTE: this issue exists because of an incomplete fix for CVE-2017-18342.

Timeline

dates in UTC
  1. 2020-02-1904:15CVE publishedNVD

Versions per branch

OSV · NVD
pyyaml
BranchAffectedFixed in
5.x≥ 5.1, < 5.25.2
5.x≥ 5.1, < 5.2b15.2b1
Pyyaml
BranchAffectedFixed in
5.1≥ 5.1, ≤ 5.1.2no fix published
Fedoraproject fedora
BranchAffectedFixed in
30.x= 30no fix published
31.x= 31no fix published

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

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

  • babelRocky Linux:8all versions · fixed in 0:2.7.0-10.module+el8.4.0+570+c2eaf144
  • babelRed Hat:enterprise_linux:8::appstreamall versions · fixed in 0:2.7.0-10.module+el8.2.0+5234+f98739b6and 1 other package
  • CythonRocky Linux:8all versions · fixed in 0:0.29.14-4.module+el8.4.0+570+c2eaf144
  • CythonRed Hat:enterprise_linux:8::appstreamall versions · fixed in 0:0.29.14-4.module+el8.2.0+5234+f98739b6and 3 other packages
  • mod_wsgiRocky Linux:8all versions · fixed in 0:4.6.8-3.module+el8.4.0+570+c2eaf144
  • mod_wsgiRed Hat:enterprise_linux:8::appstreamall versions · fixed in 0:4.6.8-3.module+el8.2.0+5234+f98739b6and 1 other package
  • numpyRocky Linux:8all versions · fixed in 0:1.17.3-5.module+el8.4.0+570+c2eaf144
  • python-asn1cryptoRocky Linux:8all versions · fixed in 0:1.2.0-3.module+el8.4.0+570+c2eaf144

63 more package ranges on OSV.dev

Vendor advisories

  • CVE-2019-20477 Red Hat Product Security232 products fixed · 3 known affected

    PyYAML: command execution through python/object/apply constructor in FullLoader

    PyYAML.src as a component of Red Hat Enterprise Linux 6 · PyYAML.src as a component of Red Hat OpenStack Platform 10 (Newton) · PyYAML.src as a component of Red Hat OpenStack Platform 13 (Queens)

  • RHSA-2021:0420 Red Hat Product Security11 products fixed

    Red Hat Security Advisory: Red Hat Quay v3.4.0 security update

  • RHSA-2020:4641 Red Hat Product Security221 products fixed

    Red Hat Security Advisory: python38:3.8 security, bug fix, and enhancement update

Full record on NVD

Fix

  1. Update pyyaml to 5.2 · 5.2b1
  2. Vendor fix Red Hat Product Security RHSA-2021:0420 · 11 productsBefore applying this update, make sure all previously released errata relevant to your system have been applied. For details on how to apply this update, refer to: https://access.redhat.com/articles/11258
  3. Vendor fix Red Hat Product Security RHSA-2020:4641 · 221 productsFor details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258
  4. Workaround from the vendor Red Hat Product Security RHSA-2021:0420 · 11 productsUse `yaml.safe_load` or the SafeLoader loader when you parse untrusted input.
  5. No fix planned, says the vendor Red Hat Product Security CVE-2019-20477 · 1 productOut of support scope
  6. No fix planned, says the vendor Red Hat Product Security CVE-2019-20477 · 2 productsWill not fix

Advisories and patches

Detection

Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof of concept
Metasploit modules
none listed
Metasploit Framework

Sources

  • NVDCVSS 3.19.8read 2026-10-23
  • NVDCVSS 2.07.5read 2026-10-23
  • NVDweakness (CWE)CWE-502read 2026-10-23
  • FIRST EPSSEPSS score5.1 %2026-11-08
  • OSVaffected packages—
  • GitHub AdvisoriesadvisoryCRITICAL2021-04-08

Identifiers

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
2020-02-19
Last Modified
2026-06-17
NVD status
Modified
GitHub Advisory
GHSA-3pqx-4fqf-j49f

Frequently asked questions

What is CVE-2019-20477?

PyYAML 5.1 through 5.1.2 has insufficient restrictions on the load and load_all functions because of a class deserialization issue, e.g., Popen is a class in the subprocess module. NOTE: this issue exists because of an incomplete fix for CVE-2017-18342.

Is CVE-2019-20477 actively exploited?

Active exploitation of CVE-2019-20477 has not been confirmed. Its EPSS score was 5.1% on 2026-11-08, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2019-20477?

CVE-2019-20477 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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