A libx11 security update has been released for Debian GNU/Linux 9 LTS to address an integer overflow in the init_om function of libX11.

DLA 2361-1: libx11 security update

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Debian LTS Advisory DLA-2361-1 debian-lts@lists.debian.org
  https://www.debian.org/lts/security/ Emilio Pozuelo Monfort
September 01, 2020   https://wiki.debian.org/LTS
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Package : libx11
Version : 2:1.6.4-3+deb9u3
CVE ID : CVE-2020-14363
Debian Bug : 969008

Jayden Rivers found an integer overflow in the init_om function of
libX11, the X11 client-side library, which could lead to a double
free.

For Debian 9 stretch, this problem has been fixed in version
2:1.6.4-3+deb9u3.

We recommend that you upgrade your libx11 packages.

For the detailed security status of libx11 please refer to
its security tracker page at:
  https://security-tracker.debian.org/tracker/libx11

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