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Fencer Intel
critical 9.8

CVE-2017-18342 json

PyYAML insecurely deserializes YAML strings leading to arbitrary code execution

published 2018-06-27 8 y ago modified 2026-07-01 4 mo ago also GHSA-rprw-h62v-c2w7 , PYSEC-2018-49 , EUVD-2018-0128

cvss
9.8
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
5.6%
EPSS 5.6% chance of exploitation in 30 days, percentile 92%
public exploits
0
none known

Summary

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.

Patch / fix

  • pypi pyyaml 5.1
  • pyyaml pyyaml 5.1
  • pyyaml Debian 14, Debian 13, Debian 12 5.1.2-1

debian advisories DEBIAN-CVE-2017-18342

  • python-PyYAML openSUSE Tumbleweed 6.0.3-1.6
  • python-openapi-spec-validator openSUSE Tumbleweed 0.9.0-1.1
  • python-openapi-spec-validator openSUSE Tumbleweed 0.7.1-1.3
  • python-PyYAML openSUSE Tumbleweed 6.0.1-4.1
  • oci-cli openSUSE Tumbleweed 3.0.2-1.2
  • python-PyYAML openSUSE Tumbleweed 5.4.1-1.6

opensuse advisories openSUSE-SU-2026:11996-1openSUSE-SU-2026:11192-1openSUSE-SU-2024:14152-1openSUSE-SU-2024:14089-1openSUSE-SU-2024:11108-1openSUSE-SU-2024:11210-1

  • python-yaml Arch Linux 5.1-1

arch linux advisories AVG-843

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2017-18342 updated cvss 9.8

PyYAML: yaml.load() API could execute arbitrary code

  • Red Hat Ceph Storage 1.3 PyYAML Red Hat Enterprise Linux 6 PyYAML Red Hat Enterprise Linux 7 PyYAML Red Hat Enterprise Linux 8 PyYAML, python2-pyyaml, python38-pyyaml, python39-pyyaml Red Hat Enterprise Linux OpenStack Platform 7 (Kilo) PyYAML Red Hat Enterprise MRG 2 PyYAML
    +7 more products
    Red Hat OpenStack Platform 8 (Liberty) PyYAML Red Hat OpenStack Platform 9 (Mitaka) PyYAML Red Hat OpenStack Platform 10 (Newton) PyYAML Red Hat OpenStack Platform 12 (Pike) PyYAML Red Hat OpenStack Platform 13 (Queens) PyYAML Red Hat Satellite 5 PyYAML Red Hat Software Collections python27-PyYAML, rh-python36-PyYAML
    affected: workaround, no fix planned “Will not fix”
  • Red Hat OpenStack Platform 15 (Stein) PyYAML
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

5.57% chance of exploitation in the next 30 days, higher than 92% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by version score vector
NVD 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD 2.0 7.5 AV:N/AC:L/Au:N/C:P/I:P/A:P
GitHub 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected packages

ecosystem package affected fixed in
pypi pyyaml
<5.1
5.1

Classification

Weakness
  • CWE-502 Deserialization of Untrusted Data

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.