A libssh security update has been released for Debian GNU/Linux 9 LTS to address a denial-of-service.

DLA 2303-1: libssh security update

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Debian LTS Advisory DLA-2303-1 debian-lts@lists.debian.org
  https://www.debian.org/lts/security/ Markus Koschany
July 31, 2020   https://wiki.debian.org/LTS
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Package : libssh
Version : 0.7.3-2+deb9u3
CVE ID : CVE-2020-16135

The code in src/sftpserver.c did not verify the validity of certain
pointers and expected them to be valid. A NULL pointer dereference could
have been occurred that typically causes a crash and thus a
denial-of-service.

For Debian 9 stretch, this problem has been fixed in version
0.7.3-2+deb9u3.

We recommend that you upgrade your libssh packages.

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

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