A shadow security update has been released for Debian GNU/Linux 9 LTS to address several vulnerabilities.

DLA 2596-1: shadow security update

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Debian LTS Advisory DLA-2596-1 debian-lts@lists.debian.org
  https://www.debian.org/lts/security/ Sylvain Beucler
March 17, 2021   https://wiki.debian.org/LTS
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Package : shadow
Version : 1:4.4-4.1+deb9u1
CVE ID : CVE-2017-12424 CVE-2017-20002
Debian Bug : 756630 914957

Several vulnerabilities were discovered in the shadow suite of login
tools. An attacker may escalate privileges in specific configurations.

CVE-2017-20002

Shadow incorrectly lists pts/0 and pts/1 as physical terminals in
/etc/securetty. This allows local users to login as password-less
users even if they are connected by non-physical means such as SSH
(hence bypassing PAM's nullok_secure configuration). This notably
affects environments such as virtual machines automatically
generated with a default blank root password, allowing all local
users to escalate privileges. It should be noted however that
/etc/securetty will be dropped in Debian 11/bullseye.

CVE-2017-12424

The newusers tool could be made to manipulate internal data
structures in ways unintended by the authors. Malformed input may
lead to crashes (with a buffer overflow or other memory
corruption) or other unspecified behaviors. This crosses a
privilege boundary in, for example, certain web-hosting
environments in which a Control Panel allows an unprivileged user
account to create subaccounts.

For Debian 9 stretch, these problems have been fixed in version
1:4.4-4.1+deb9u1.

We recommend that you upgrade your shadow packages.

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

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