A x11vnc security update has been released for Debian GNU/Linux 9 LTS to address a flaw that could be used to remote access to an existing X session.

DLA 2490-1: x11vnc security update

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Debian LTS Advisory DLA-2490-1 debian-lts@lists.debian.org
  https://www.debian.org/lts/security/ Thorsten Alteholz
December 10, 2020   https://wiki.debian.org/LTS
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Package : x11vnc
Version : 0.9.13-2+deb9u2
CVE ID : CVE-2020-29074

Guenal Davalan reported a flaw in x11vnc, a VNC server to allow remote
access to an existing X session. x11vnc creates shared memory segments
with 0777 mode. A local attacker can take advantage of this flaw for
information disclosure, denial of service or interfering with the VNC
session of another user on the host.

For Debian 9 stretch, this problem has been fixed in version
0.9.13-2+deb9u2.

We recommend that you upgrade your x11vnc packages.

For the detailed security status of x11vnc please refer to
its security tracker page at:
  https://security-tracker.debian.org/tracker/x11vnc

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