What’s Vulnerable › Vulnerabilities

CVE-2018-20021

• Severity: high (CVSS 7.5 v3.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 3.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2018-12-19 · updated 2026-06-17
• Weakness: CWE-835

Description

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

Affected products

• Canonical Ubuntu Linux: 14.04, 16.04, 18.04, 18.10
• Debian Linux: 8.0, 9.0
• Libvnc Project Libvncserver: before 0.9.12 — fixed in 0.9.12

How to fix

Upgrade to a fixed version: Libvnc Project Libvncserver 0.9.12. Check the vendor advisory for mitigations.

References

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

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