HOMEVULNERABILITIESCVE-2019-20840
HIGH

CVE-2019-20840

CWE-787Published: June 17, 2020· Updated: Jun 17, 2026

7.5
CVSS v3.1

Official Description

An issue was discovered in LibVNCServer before 0.9.13. libvncserver/ws_decode.c can lead to a crash because of unaligned accesses in hybiReadAndDecode.

NVD Source

Technical Analysis

CVE-2019-20840 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.

A successful exploit results in availability disruption (denial of service), with a CVSS base score of 7.5.

From a weakness classification perspective (CWE-787): Out-of-bounds write vulnerabilities can lead to data corruption, crashes, or arbitrary code execution.

CVSS v3.1 Vector Breakdown

Exploitability
Attack VectorNetwork
Attack ComplexityLow
Privileges Req.None
User InteractionNone
ScopeUnchanged
Impact
ConfidentialityNone
IntegrityNone
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected Vendors & Products

Canonical1 product(s)
ubuntu linux
Debian1 product(s)
debian linux
libvnc_project1 product(s)
libvncserver
openSUSE1 product(s)
leap
siemens12 product(s)
simatic itc1500 firmwaresimatic itc1500simatic itc1500 pro firmwaresimatic itc1500 prosimatic itc1900 firmwaresimatic itc1900simatic itc1900 pro firmwaresimatic itc1900 prosimatic itc2200 firmwaresimatic itc2200simatic itc2200 pro firmwaresimatic itc2200 pro
Source: NVD CPE · 21 total CPE entries

Exploit & PoC Resources

NO KNOWN EXPLOITNo public exploit confirmed at this time
Exploit-DB
Offensive Security exploit database
GitHub PoC Search
Community PoC repositories
Rapid7 / Metasploit
Metasploit module search
PacketStorm
Security advisories & exploits
NVD Detail
Official NIST entry
MITRE CVE
CVE Program entry
External links open in a new tab. Always verify in a controlled environment before use.

Official Patches & Advisories

PATCHhttps://cert-portal.siemens.com/productcert/pdf/ssa-390195.pdf
PATCHhttps://github.com/LibVNC/libvncserver/commit/0cf1400c61850065de590d403f6d49e32882fd76
PATCHhttps://cert-portal.siemens.com/productcert/pdf/ssa-390195.pdf
PATCHhttps://github.com/LibVNC/libvncserver/commit/0cf1400c61850065de590d403f6d49e32882fd76
ADVISORYhttp://lists.opensuse.org/opensuse-security-announce/2020-07/msg00033.html
ADVISORYhttp://lists.opensuse.org/opensuse-security-announce/2020-07/msg00055.html
ADVISORYhttp://lists.opensuse.org/opensuse-security-announce/2020-07/msg00066.html
ADVISORYhttps://github.com/LibVNC/libvncserver/compare/LibVNCServer-0.9.12...LibVNCServer-0.9.13
ADVISORYhttps://usn.ubuntu.com/4434-1/
ADVISORYhttp://lists.opensuse.org/opensuse-security-announce/2020-07/msg00033.html
ADVISORYhttp://lists.opensuse.org/opensuse-security-announce/2020-07/msg00055.html
ADVISORYhttp://lists.opensuse.org/opensuse-security-announce/2020-07/msg00066.html
ADVISORYhttps://github.com/LibVNC/libvncserver/compare/LibVNCServer-0.9.12...LibVNCServer-0.9.13
ADVISORYhttps://usn.ubuntu.com/4434-1/

All References (16)

→
http://lists.opensuse.org/opensuse-security-announce/2020-07/msg00033.htmlMailing List · Third Party Advisory
→
http://lists.opensuse.org/opensuse-security-announce/2020-07/msg00055.htmlMailing List · Third Party Advisory
→
http://lists.opensuse.org/opensuse-security-announce/2020-07/msg00066.htmlMailing List · Third Party Advisory
→
https://cert-portal.siemens.com/productcert/pdf/ssa-390195.pdfPatch · Third Party Advisory
→
https://github.com/LibVNC/libvncserver/commit/0cf1400c61850065de590d403f6d49e32882fd76Patch · Third Party Advisory
→
https://github.com/LibVNC/libvncserver/compare/LibVNCServer-0.9.12...LibVNCServer-0.9.13Release Notes · Third Party Advisory
→
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/4F6FUH4EFK4NAP6GT4TQRTBKWIRCZLIY/
→
https://usn.ubuntu.com/4434-1/Third Party Advisory
→
http://lists.opensuse.org/opensuse-security-announce/2020-07/msg00033.htmlMailing List · Third Party Advisory
→
http://lists.opensuse.org/opensuse-security-announce/2020-07/msg00055.htmlMailing List · Third Party Advisory
→
http://lists.opensuse.org/opensuse-security-announce/2020-07/msg00066.htmlMailing List · Third Party Advisory
→
https://cert-portal.siemens.com/productcert/pdf/ssa-390195.pdfPatch · Third Party Advisory
→
https://github.com/LibVNC/libvncserver/commit/0cf1400c61850065de590d403f6d49e32882fd76Patch · Third Party Advisory
→
https://github.com/LibVNC/libvncserver/compare/LibVNCServer-0.9.12...LibVNCServer-0.9.13Release Notes · Third Party Advisory
→
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/4F6FUH4EFK4NAP6GT4TQRTBKWIRCZLIY/

Quick Facts

CVE IDCVE-2019-20840
CVSS Score7.5 / 10
SeverityHIGH
WeaknessCWE-787
CISA KEVNo
Affected5 vendor(s)
PublishedJun 17, 2020

Related CVEs (CWE-787)

CVE-2002-2227
10.0
CVE-2014-1478
10.0
CVE-2018-10718
10.0
CVE-2026-42369
10.0
CVE-2012-0751
10.0
CVE-2018-17160
10.0

Recommended Actions

  • →Apply vendor patches immediately
  • →Monitor CVE-2019-20840 in threat intel feeds
  • →Review IDS/IPS signatures for exploitation attempts
Data sourced from NVD (NIST), CISA KEV, and EPSS (FIRST). Analysis generated by CTIWatch. CVE data is provided under the NVD usage policy.
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