A sudo security update has been released for Debian GNU/Linux 9 LTS to address a heap-based buffer overflow vulnerability.

DLA 2534-1: sudo security update

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Debian LTS Advisory DLA-2534-1 debian-lts@lists.debian.org
  https://www.debian.org/lts/security/ Salvatore Bonaccorso
January 26, 2021   https://wiki.debian.org/LTS
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Package : sudo
Version : 1.8.19p1-2.1+deb9u3
CVE ID : CVE-2021-3156

The Qualys Research Labs discovered a heap-based buffer overflow
vulnerability in sudo, a program designed to provide limited super user
privileges to specific users. Any local user (sudoers and non-sudoers)
can exploit this flaw for root privilege escalation.

For Debian 9 stretch, this problem has been fixed in version
1.8.19p1-2.1+deb9u3.

We recommend that you upgrade your sudo packages.

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

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