An usermode bugfix update has been released for Debian GNU/Linux 9 LTS to address an upgrade issue when upgrading from Debian 7.

BUGFIX: DLA 2744-1: usermode upgrade issues

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Debian LTS Advisory DLA-2744-1 debian-lts@lists.debian.org
  https://www.debian.org/lts/security/ Utkarsh Gupta
August 16, 2021   https://wiki.debian.org/LTS
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Package : usermode
Version : 1.109-1+deb9u1
Debian Bug : 991808

This update is merely a rebuild of the usermode package, which are
a set of graphical tools for certain user account management tasks,
fixing two issues:

a) the versioning issue as wheezy (Debian 7) had a greater version
than jessie (Debian 8) and stretch (Debian 9), thereby causing
upgrade issues.
b) the package now Depends and Build-Depends on the newer
libuser1-dev (>= 1:0.62~dfsg-0.1) to ensure the latest
version of libuser is used (which was a security fix).

For Debian 9 stretch, this problem has been fixed in version
1.109-1+deb9u1.

We recommend that you upgrade your usermode packages.

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