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CVE-2018-20021

25
FAUCET Score

CVE-2018-20021 is an infinite loop vulnerability (CWE-835) in LibVNC client code, affecting various Canonical and Debian Linux distributions and their LibVNCServer packages. This flaw allows an attacker to trigger excessive resource consumption (CPU, RAM) on vulnerable systems. With a CVSS score of 7.5 (High), it presents a significant availability risk, as it can be exploited remotely without authentication or user interaction. While there is no known active exploitation, public exploit code, or KEV listing, the vulnerability has garnered some community discussion and media coverage, indicating awareness within the cybersecurity community.

Impacted Technologies

VendorProductVersion(s)CPE
< 0.9.12CPE matchmatch criteria
cpe:2.3:a:libvnc_project:libvncserver:*:*:*:*:*:*:*:*
14.04CPE matchmatch criteria
cpe:2.3:o:canonical:ubuntu_linux:14.04:*:*:*:lts:*:*:*
16.04CPE matchmatch criteria
cpe:2.3:o:canonical:ubuntu_linux:16.04:*:*:*:lts:*:*:*
18.04CPE matchmatch criteria
cpe:2.3:o:canonical:ubuntu_linux:18.04:*:*:*:lts:*:*:*
18.10CPE matchmatch criteria
cpe:2.3:o:canonical:ubuntu_linux:18.10:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.0

7.5HIGH

CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
NONE
Integrity Impact
NONE
Availability Impact
HIGH
Exploitability Score
3.9
Impact Score
3.6
CvssVersion
3.0

Exploit Intelligence

EPSS Score
3.52%
Probability of exploitation in next 30 days
EPSS Percentile
88.0%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0352 is in the 79th percentile among its peer group of 51,551 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.1 Bluesky, 0.1 Mastodon, and 0.4 GitHub mentions.

Media Mentions

The average CVE in this peer group has 0.1 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Vendor Patches (1)

redhatend of lifevia redhat_api
Product: Red Hat Enterprise Linux 8Fixed in: libvncserver

Vendor Advisories (1)

redhatCVE-2018-20021Low

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

Dec 19, 2018

References

ics-cert.kaspersky.com / advisories/klcert-advisories/2018/12/19/klcert-18-031-libvnc-infinite-loop
Third Party Advisory
lists.debian.org / debian-lts-announce/2018/12/msg00017.html
Mailing ListThird Party Advisory
lists.debian.org / debian-lts-announce/2019/10/msg00042.html
lists.debian.org / debian-lts-announce/2019/11/msg00033.html
lists.debian.org / debian-lts-announce/2019/12/msg00028.html
security.gentoo.org / glsa/201908-05
security.gentoo.org / glsa/202006-06
usn.ubuntu.com / 3877-1
Third Party Advisory
usn.ubuntu.com / 4547-1
usn.ubuntu.com / 4547-2
usn.ubuntu.com / 4587-1
debian.org / security/2019/dsa-4383
Third Party Advisory