A lxml regression update has been released for Debian GNU/Linux 9 LTS to address a regression introduces by the previous update.

DLA 2467-2: lxml regression update

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Debian LTS Advisory DLA-2467-2 debian-lts@lists.debian.org
  https://www.debian.org/lts/security/ Roberto C. Sánchez
December 18, 2020   https://wiki.debian.org/LTS
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Package : lxml
Version : 3.7.1-1+deb9u3
CVE ID : CVE-2020-27783

The fix for CVE-2020-27783, released as DLA 2467-1, was incomplete as
the component was still affected by the vulnerability. This
update includes an additional patch that completes the fix. Note that a
package with version 3.7.1-1+deb9u2 was uploaded, but before the
publication of the advisory a regression was discovered, which was
immediately corrected prior to publication of this advisory.

For Debian 9 stretch, this problem has been fixed in version
3.7.1-1+deb9u3.

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