A lxml security update has been released for Debian GNU/Linux 9 LTS to address an issue where the HTML Cleaner in lxml.html lets certain crafted script content pass through.

DLA 2871-1: lxml security update

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Debian LTS Advisory DLA-2871-1 debian-lts@lists.debian.org
  https://www.debian.org/lts/security/ Utkarsh Gupta
December 30, 2021   https://wiki.debian.org/LTS
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Package : lxml
Version : 3.7.1-1+deb9u5
CVE ID : CVE-2021-43818
Debian Bug : 1001885

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.

For Debian 9 stretch, this problem has been fixed in version
3.7.1-1+deb9u5.

We recommend that you upgrade your lxml packages.

For the detailed security status of lxml please refer to
its security tracker page at:
  https://security-tracker.debian.org/tracker/lxml

Further information about Debian LTS security advisories, how to apply
these updates to your system and frequently asked questions can be
found at:   https://wiki.debian.org/LTS