A rxvt-unicode security update has been released for Debian GNU/Linux 9 LTS to address an improper handling of certain escape sequences.

DLA 2671-1: rxvt-unicode security update

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Debian LTS Advisory DLA-2671-1 debian-lts@lists.debian.org
  https://www.debian.org/lts/security/ Utkarsh Gupta
May 30, 2021   https://wiki.debian.org/LTS
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Package : rxvt-unicode
Version : 9.22-1+deb9u1
CVE ID : CVE-2021-33477
Debian Bug : 988763

rxvt-unicode allow (potentially remote) code execution because of
improper handling of certain escape sequences (ESC G Q). A response is
terminated by a newline.

For Debian 9 stretch, this problem has been fixed in version
9.22-1+deb9u1.

We recommend that you upgrade your rxvt-unicode packages.

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

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