Pavel Cheremushkin discovered several vulnerabilities in libvncserver, a library to implement VNC server/client functionalities, which might result in the execution of arbitrary code, denial of service or information disclosure.
For the stable distribution (stretch), these problems have been fixed in version 0.9.11+dfsg-1.3~deb9u1.
We recommend that you upgrade your libvncserver packages.
Further information about Debian Security Advisories, how to apply these updates to your system and frequently asked questions can be found at: https://www.debian.org/security/