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Fencer Intel
high 7.5

CVE-2018-20021 json

LibVNC before commit c3115350eb8bb635d0fdb4dbbb0d0541f38ed19c contains a CWE-835: Infinite loop vulnerability in VNC client code.

published 7y ago modified 4mo ago also EUVD-2018-12599

cvss
7.5
version 3.0, NVD
cisa kev
Not listed
not in CISA's catalog
epss
3.4%
EPSS 3.4% chance of exploitation in 30 days, percentile 88%
public exploits
0
none known

Summary

LibVNC before commit c3115350eb8bb635d0fdb4dbbb0d0541f38ed19c contains a CWE-835: Infinite loop vulnerability in VNC client code. Vulnerability allows attacker to consume excessive amount of resources like CPU and RAM

Patch / fix

  • libvnc_project libvncserver 0.9.12
  • ssvnc Debian 14, Debian 13, Debian 12 1.0.29-5
  • veyon Debian 13, Debian 12 4.1.4+repack1-1
  • tightvnc Debian 14, Debian 13, Debian 12 1:1.3.9-9.1
  • libvncserver Debian 14, Debian 13, Debian 12 0.9.11+dfsg-1.2

debian advisories DEBIAN-CVE-2018-20021

  • italc Ubuntu 16.04 LTS 1:2.0.2+dfsg1-4ubuntu0.1
  • italc Ubuntu 18.04 LTS 1:3.0.3+dfsg1-3ubuntu0.1
  • ssvnc Ubuntu 16.04 LTS 1.0.29-2+deb8u1build0.16.04.1
  • libvncserver Ubuntu 14.04 LTS 0.9.9+dfsg-1ubuntu1.4
  • libvncserver Ubuntu 16.04 LTS 0.9.10+dfsg-3ubuntu0.16.04.3
  • libvncserver Ubuntu 18.04 LTS 0.9.11+dfsg-1ubuntu1.1
  • tightvnc Ubuntu Pro 14.04 LTS 1.3.9-6.5+deb8u1build0.14.04.1~esm1

ubuntu advisories UBUNTU-CVE-2018-20021

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • LibVNCServer SLES 12 SP4, SLES 12 SP3, SLES 12 SP2-BCL +11 more 0.9.9-17.8.1
  • LibVNCServer SLE Workstation Extension 15, SLE Module for Package Hub 15 0.9.10-4.3.1
  • LibVNCServer SLES for SAP 11 SP4, SLES 11 SP4, SLES 11 SP3-TERADATA +3 more 0.9.1-160.6.1

suse advisories SUSE-SU-2019:0060-2SUSE-SU-2019:0080-1SUSE-SU-2019:13927-1SUSE-SU-2019:0060-1

  • LibVNCServer openSUSE Leap 15.0 0.9.10-lp150.3.3.1

opensuse advisories openSUSE-SU-2019:0053-1

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Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2018-20021 updated cvss 6.5

libvncserver: Infinite loop in VNC client code allows for denial of service

  • Red Hat Enterprise Linux 8 libvncserver
    affected: no fix planned “Will not fix”
  • Red Hat Enterprise Linux 6 libvncserver Red Hat Enterprise Linux 7 libvncserver
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

3.42% chance of exploitation in the next 30 days, higher than 88% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by version score vector
NVD 3.0 7.5 CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD 2.0 7.8 AV:N/AC:L/Au:N/C:N/I:N/A:C

Affected products

  • n/a LibVNC

Classification

Weakness
  • CWE-835 Loop with Unreachable Exit Condition

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.