A libx11 security update has been released for Debian GNU/Linux 10 to address a protocol command injection vulnerability.

DSA 4920-1: libx11 security update

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Debian Security Advisory DSA-4920-1 security@debian.org
  https://www.debian.org/security/ Salvatore Bonaccorso
May 24, 2021   https://www.debian.org/security/faq
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Package : libx11
CVE ID : CVE-2021-31535
Debian Bug : 988737

Roman Fiedler reported that missing length validation in various
functions provided by libx11, the X11 client-side library, allow
to inject X11 protocol commands on X clients, leading to
authentication bypass, denial of service or potentially the
execution of arbitrary code.

For the stable distribution (buster), this problem has been fixed in
version 2:1.6.7-1+deb10u2.

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 Security Advisories, how to apply
these updates to your system and frequently asked questions can be
found at:   https://www.debian.org/security/