---
id: CVE-2021-43818
aliases:
  - GHSA-55x5-fj6c-h6m8
  - PYSEC-2021-852
title: lxml's HTML Cleaner allows crafted and SVG embedded scripts to pass through
summary: lxml's HTML Cleaner allows crafted and SVG embedded scripts to pass through
severity: high
cvss: 8.2
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:N'
vendor: lxml
product: lxml
ecosystem: pip
affected:
  - lxml < 4.6.5
patched:
  - lxml 4.6.5
published: '2021-12-13'
updated: '2026-07-08'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GHSA-55x5-fj6c-h6m8'
references:
  - url: 'https://github.com/lxml/lxml/security/advisories/GHSA-55x5-fj6c-h6m8'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2021-43818'
  - url: >-
      https://github.com/lxml/lxml/commit/12fa9669007180a7bb87d990c375cf91ca5b664a
  - url: >-
      https://github.com/lxml/lxml/commit/a3eacbc0dcf1de1c822ec29fb7d090a4b1712a9c#diff-59130575b4fb2932c957db2922977d7d89afb0b2085357db1a14615a2fcad776
  - url: >-
      https://github.com/lxml/lxml/commit/f2330237440df7e8f39c3ad1b1aa8852be3b27c0
  - url: 'https://www.oracle.com/security-alerts/cpujul2022.html'
  - url: 'https://www.oracle.com/security-alerts/cpuapr2022.html'
  - url: 'https://www.debian.org/security/2022/dsa-5043'
  - url: 'https://security.netapp.com/advisory/ntap-20220107-0005'
  - url: 'https://security.gentoo.org/glsa/202208-06'
  - url: >-
      https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/ZQ4SPKJX3RRJK4UWA6FXCRHD2TVRQI44
  - url: >-
      https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/WZGNET2A4WGLSUXLBFYKNC5PXHQMI3I7
  - url: >-
      https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/V2XMOM5PFT6U5AAXY6EFNT5JZCKKHK2V
  - url: >-
      https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/TUIS2KE3HZ2AAQKXFLTJFZPP2IFHJTC7
  - url: 'https://lists.debian.org/debian-lts-announce/2021/12/msg00037.html'
  - url: >-
      https://github.com/pypa/advisory-database/tree/main/vulns/lxml/PYSEC-2021-852.yaml
  - url: 'https://github.com/lxml/lxml'
tags:
  - osv
  - pip
epss: 0.02477
epssPercentile: 0.83865
ingestedAt: '2026-07-08T18:25:45.783Z'
---

## Overview

### Impact
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.

### Patches
The issue has been resolved in lxml 4.6.5.

### Workarounds
None.

### References
The issues are tracked under the report IDs GHSL-2021-1037 and GHSL-2021-1038.


## Affected packages

- `lxml < 4.6.5`

## Remediation

Upgrade to a patched release:

- `lxml 4.6.5`