An icu security update has been released for Debian GNU/Linux 9 LTS to address a potential use-after-free vulnerability.

DLA 2784-1: icu security update

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Debian LTS Advisory DLA-2784-1 debian-lts@lists.debian.org
  https://www.debian.org/lts/security/ Chris Lamb
October 12, 2021   https://wiki.debian.org/LTS
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Package : icu
Version : 57.1-6+deb9u5
CVE ID : CVE-2020-21913

It was discovered that there was a potential use-after-free
vulnerability in icu, a library which provides Unicode and locale
functionality.

For Debian 9 "Stretch", this problem has been fixed in version
57.1-6+deb9u5.

We recommend that you upgrade your icu packages.

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

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