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Ubuntu Security Notice USN-4407-1
July 01, 2020

libvncserver vulnerabilities
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A security issue affects these releases of Ubuntu and its derivatives:

- Ubuntu 20.04 LTS
- Ubuntu 19.10
- Ubuntu 18.04 LTS
- Ubuntu 16.04 LTS

Summary:

Several security issues were fixed in LibVNCServer.

Software Description:
- libvncserver: vnc server library

Details:

It was discovered that LibVNCServer incorrectly handled decompressing
data. An
attacker could possibly use this issue to cause LibVNCServer to crash,
resulting in a denial of service. (CVE-2019-15680)

It was discovered that an information disclosure vulnerability existed in
LibVNCServer when sending a ServerCutText message. An attacker could
possibly
use this issue to expose sensitive information. This issue only affected
Ubuntu 19.10, Ubuntu 18.04 LTS, and Ubuntu 16.04 LTS. (CVE-2019-15681)

It was discovered that LibVNCServer incorrectly handled cursor shape
updates.
If a user were tricked in to connecting to a malicious server, an attacker
could possibly use this issue to cause LibVNCServer to crash, resulting in a
denial of service, or possibly execute arbitrary code. This issue only
affected Ubuntu 19.10, Ubuntu 18.04 LTS, and Ubuntu 16.04 LTS.
(CVE-2019-15690, CVE-2019-20788)

It was discovered that LibVNCServer incorrectly handled decoding WebSocket
frames. An attacker could possibly use this issue to cause LibVNCServer to
crash, resulting in a denial of service, or possibly execute arbitrary code.
This issue only affected Ubuntu 19.10, Ubuntu 18.04 LTS, and Ubuntu
16.04 LTS.
(CVE-2017-18922)

Update instructions:

The problem can be corrected by updating your system to the following
package versions:

Ubuntu 20.04 LTS:
libvncclient1 0.9.12+dfsg-9ubuntu0.1
libvncserver1 0.9.12+dfsg-9ubuntu0.1

Ubuntu 19.10:
libvncclient1 0.9.11+dfsg-1.3ubuntu0.1
libvncserver1 0.9.11+dfsg-1.3ubuntu0.1

Ubuntu 18.04 LTS:
libvncclient1 0.9.11+dfsg-1ubuntu1.2
libvncserver1 0.9.11+dfsg-1ubuntu1.2

Ubuntu 16.04 LTS:
libvncclient1 0.9.10+dfsg-3ubuntu0.16.04.4
libvncserver1 0.9.10+dfsg-3ubuntu0.16.04.4

After a standard system update you need to restart LibVNCServer to make
all the necessary changes.

References:
https://usn.ubuntu.com/4407-1
CVE-2017-18922, CVE-2019-15680, CVE-2019-15681, CVE-2019-15690,
CVE-2019-20788

Package Information:
https://launchpad.net/ubuntu/+source/libvncserver/0.9.12+dfsg-9ubuntu0.1
https://launchpad.net/ubuntu/+source/libvncserver/0.9.11+dfsg-1.3ubuntu0.1
https://launchpad.net/ubuntu/+source/libvncserver/0.9.11+dfsg-1ubuntu1.2
https://launchpad.net/ubuntu/+source/libvncserver/0.9.10+dfsg-3ubuntu0.16.04.4