Skip to content
Fencer Vulns
high 8.2

CVE-2021-43818 json

HTML Cleaner allows crafted and SVG embedded scripts to pass through

published 2021-12-13 4 y ago modified 2026-07-08 4 mo ago also GHSA-55x5-fj6c-h6m8 , PYSEC-2021-852 , EUVD-2021-0117

cvss
8.2
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
2.6%
EPSS 2.6% chance of exploitation in 30 days, percentile 85%
public exploits
0
none known

Summary

lxml is a library for processing XML and HTML in the Python language. Prior to version 4.6.5, the HTML Cleaner in lxml.html lets certain crafted script content pass through, as well as script content in SVG files embedded using data URIs. Users that employ the HTML cleaner in a security relevant context should upgrade to lxml 4.6.5 to receive a patch. There are no known workarounds available.

Patch / fix

  • pypi lxml 4.6.5
  • lxml lxml 4.6.5
  • lxml Debian 14, Debian 13, Debian 12 4.7.1-1

debian advisories DEBIAN-CVE-2021-43818

  • lxml Ubuntu 18.04 LTS 4.2.1-1ubuntu0.6
  • lxml Ubuntu 20.04 LTS 4.5.0-1ubuntu0.5
  • lxml Ubuntu 22.04 LTS 4.7.1-1
  • lxml Ubuntu Pro 14.04 LTS 3.3.3-1ubuntu0.2+esm5
  • lxml Ubuntu Pro 16.04 LTS 3.5.0-1ubuntu0.4+esm2

ubuntu advisories UBUNTU-CVE-2021-43818

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • foreman satellite utils 6.11, satellite capsule 6.11, satellite 6.11 3.1.1.21-2.el7sat
  • foreman satellite utils 6.11, satellite capsule 6.11, satellite 6.11 3.1.1.21-2.el8sat
  • libsolv satellite capsule 6.11, satellite 6.11 0.7.22-1.el7pc
  • libsolv satellite capsule 6.11, satellite 6.11 0.7.22-1.el8pc
  • candlepin satellite 6.11 4.1.13-1.el7sat
  • candlepin satellite 6.11 4.1.13-1.el8sat
  • satellite satellite utils 6.11, satellite capsule 6.11, satellite 6.11 6.11.0-2.el7sat
  • satellite satellite utils 6.11, satellite capsule 6.11, satellite 6.11 6.11.0-2.el8sat

red hat advisories RHSA-2022:5498RHSA-2022:1932RHSA-2022:1821RHSA-2022:1664RHSA-2022:1764RHSA-2022:1763

  • grafana OpenStack Cloud Crowbar 9, OpenStack Cloud 9 6.7.4-3.26.1
  • python-lxml OpenStack Cloud Crowbar 9, OpenStack Cloud 9 4.2.4-3.3.1
  • python-Pillow OpenStack Cloud Crowbar 9, OpenStack Cloud 9 5.2.0-3.17.1
  • ardana-barbican OpenStack Cloud 9 9.0+git.1644879908.8a641c1-3.13.1
  • rubygem-sinatra OpenStack Cloud Crowbar 9 1.4.6-4.3.1
  • openstack-cinder OpenStack Cloud Crowbar 9, OpenStack Cloud 9 13.0.10~dev24-3.34.2
  • openstack-ironic OpenStack Cloud Crowbar 9, OpenStack Cloud 9 11.1.5~dev18-3.28.2
  • openstack-neutron OpenStack Cloud Crowbar 9, OpenStack Cloud 9 13.0.8~dev206-3.40.1

suse advisories SUSE-SU-2022:1729-1SUSE-SU-2022:0895-1SUSE-SU-2022:0803-1

  • python-lxml openSUSE Leap 15.3 4.7.1-3.7.1

opensuse advisories openSUSE-SU-2022:0803-1

  • python3-lxml AlmaLinux 8 4.2.3-4.el8
  • babel AlmaLinux 8 2.5.1-10.module_el8.6.0+2781+fed64c13
  • python2 AlmaLinux 8 2.7.18-10.module_el8.6.0+2781+fed64c13.alma
  • python2-py AlmaLinux 8 1.5.3-6.module_el8.6.0+2781+fed64c13
  • python2-dns AlmaLinux 8 1.15.0-10.module_el8.6.0+2781+fed64c13
  • python2-pip AlmaLinux 8 9.0.3-19.module_el8.6.0+2781+fed64c13
  • python2-six AlmaLinux 8 1.11.0-6.module_el8.6.0+2781+fed64c13
  • python2-bson AlmaLinux 8 3.7.0-1.module_el8.6.0+2781+fed64c13

almalinux advisories ALSA-2022:1932ALSA-2022:1821ALSA-2022:1763ALSA-2022:1764

  • libdb Rocky Linux 8 5.3.28-42.el8_4
  • python-lxml Rocky Linux 8 4.2.3-4.el8
  • python-lxml Rocky Linux 8 4.2.3-4.module+el8.4.0+403+9ae17a31
  • pytz Rocky Linux 8 2017.2-12.module+el8.5.0+706+735ec4b3
  • pytz Rocky Linux 8 2017.2-12.module+el8.4.0+403+9ae17a31
  • babel Rocky Linux 8 2.5.1-10.module+el8.5.0+706+735ec4b3
  • numpy Rocky Linux 8 1:1.14.2-16.module+el8.5.0+706+735ec4b3
  • numpy Rocky Linux 8 1:1.14.2-16.module+el8.4.0+403+9ae17a31

rocky linux advisories RLSA-2022:5498RLSA-2022:1932RLSA-2022:1821RLSA-2022:1763RLSA-2022:1764

  • py3-lxml Alpine 3.24, Alpine 3.23, Alpine 3.22 +7 more 4.6.5-r0

alpine advisories ALPINE-CVE-2021-43818

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • python-lxml CBL-Mariner 2.0 4.8.0-1

azure linux advisories AZL-7025

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

  • python-lxml Arch Linux 4.6.5-1

arch linux advisories AVG-2629

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-2021-43818 updated cvss 8.8

python-lxml: HTML Cleaner allows crafted and SVG embedded scripts to pass through

  • Red Hat Ansible Automation Platform 1.2 lxml Red Hat Ansible Automation Platform 2 lxml Red Hat Ansible Tower 3 lxml
    affected: workaround, no fix available
  • Red Hat Enterprise Linux 6 python-lxml Red Hat Enterprise Linux 7 python-lxml Red Hat OpenStack Platform 13 (Queens) python-lxml
    affected: workaround, no fix planned “Out of support scope”
  • Red Hat Update Infrastructure 3 for Cloud Providers python-lxml
    affected: workaround, no fix available
  • Red Hat Enterprise Linux AppStream (v. 8) python-lxml 4.2.3-4.el8, python3-lxml 4.2.3-4.el8, pytz 2019.3-3.module+el8.4.0+8888+89bc7e79, scipy 1.3.1-4.module+el8.4.0+8888+89bc7e79, scipy 1.5.4-3.module+el8.4.0+9822+20bf1249, pytz 2017.2-12.module+el8.1.0+3111+de3f2d8e, +205 more
    fixed: vendor fix RHSA-2022:1821
  • Red Hat Satellite 6.11 for RHEL 8 python-lxml 4.7.1-1.el8pc
    fixed: vendor fix RHSA-2022:5498
  • Red Hat Software Collections for RHEL Workstation(v. 7) rh-python38-python-lxml 4.4.1-8.el7 Red Hat Software Collections for RHEL(v. 7) rh-python38-python-lxml 4.4.1-8.el7
    fixed: vendor fix RHSA-2022:1664
  • Red Hat Enterprise Linux 8 python-lxml, python3-lxml Red Hat Enterprise Linux 9 python-lxml, python3-lxml Red Hat Enterprise Linux CRB (v. 8) pytest 4.6.6-3.module+el8.4.0+8888+89bc7e79, pytest 6.0.2-2.module+el8.4.0+9822+20bf1249, Cython 0.29.21-5.module+el8.4.0+9822+20bf1249, pybind11 2.7.1-1.module+el8.6.0+12838+640e6226, python-py 1.8.0-8.module+el8.4.0+8888+89bc7e79, python-py 1.10.0-1.module+el8.4.0+9822+20bf1249, +34 more Red Hat Satellite 6.11 for RHEL 7 tfm 7.0-1.el7sat, gofer 2.12.5-7.el7sat, katello 4.3.0-3.el7sat, libsolv 0.7.22-1.el7pc, libcomps 0.1.18-1.el7pc, libsolv0 0.6.34-4.el7sat, +638 more Red Hat Satellite 6.11 for RHEL 8 libdb 5.3.28-42.el8_4, katello 4.3.0-3.el8sat, libsolv 0.7.22-1.el8pc, libcomps 0.1.18-1.el8pc, python-idna 3.3-1.el8pc, python-pbr 5.6.0-1.el8pc, +628 more Red Hat Software Collections for RHEL Workstation(v. 7) rh-python38-python 3.8.13-1.el7, rh-python38-python-pip 19.3.1-3.el7, rh-python38-python-idle 3.8.13-1.el7, rh-python38-python-libs 3.8.13-1.el7, rh-python38-python-test 3.8.13-1.el7, rh-python38-python-tkinter 3.8.13-1.el7, +3 more
    +1 more products
    Red Hat Software Collections for RHEL(v. 7) rh-python38-python 3.8.13-1.el7, rh-python38-python-pip 19.3.1-3.el7, rh-python38-python-idle 3.8.13-1.el7, rh-python38-python-libs 3.8.13-1.el7, rh-python38-python-test 3.8.13-1.el7, rh-python38-python-tkinter 3.8.13-1.el7, +3 more
    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

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
10 mo ago

Exploit prediction

2.64% chance of exploitation in the next 30 days, higher than 85% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 8.2 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:N
NVD 3.1 7.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:L
NVD 2.0 6.8 AV:N/AC:M/Au:N/C:P/I:P/A:P
GitHub 3.1 8.2 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:N

Affected packages

ecosystem package affected fixed in
pypi lxml
<4.6.5
4.6.5

Affected products

  • lxml lxml

Classification

Weakness
  • CWE-74 Improper Neutralization of Special Elements in Output Used by a Downstream Component
  • CWE-79 Improper Neutralization of Input During Web Page Generation

References

Sources

Fencer Vulns 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.