A libzstd security update has been released for Debian GNU/Linux 9 LTS to address a race condition.

DLA 2573-1: libzstd security update

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Debian LTS Advisory DLA-2573-1 debian-lts@lists.debian.org
  https://www.debian.org/lts/security/ Utkarsh Gupta
February 20, 2021   https://wiki.debian.org/LTS
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Package : libzstd
Version : 1.1.2-1+deb9u1
Debian Bug : 981404 982519

It was discovered that zstd, a compression utility, was vulnerable
to a race condition: it temporarily exposed, during a very short
timeframe, a world-readable version of its input even if the
original file had restrictive permissions.

For Debian 9 stretch, this problem has been fixed in version
1.1.2-1+deb9u1.

We recommend that you upgrade your libzstd packages.

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

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