Ubuntu LinuxOperating system · Canonical
CVE-2018-20021
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedLibVNC 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
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · moderate confidenceLibVNC client contains an infinite loop vulnerability (CWE-835) that allows a malicious VNC server to trigger excessive resource consumption (CPU and RAM) on the client side. The vulnerability exists in the client's handling of certain VNC protocol messages or state transitions, causing the client to enter an unrecoverable loop.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data
Ubuntu LinuxOperating system
= 14.04= 16.04= 18.04= 18.10
Debian LinuxOperating system
= 8.0= 9.0< 0.9.12CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify installed LibVNC packagesRun 'dpkg -l | grep -i vnc' on Debian/Ubuntu, or 'rpm -qa | grep -i vnc' on RHEL-based systems, to list installed VNC-related packagesAffected if Packages named libvncclient, libvncserver, or vinagre are installed
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Check LibVNC library versionRun 'dpkg -s libvncclient0' (Ubuntu) or 'dpkg -s libvncserver0' (Debian) and examine the Version field, or use 'apt show libvncclient'Affected if The reported version is lower than 0.9.12 (e.g., 0.9.11, 0.9.10, etc.)
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Verify VNC client applications in useRun 'ps aux | grep -E "vnc|remmina|vinagre"' to list running VNC client processes, or check installed binaries with 'which vncviewer remmina'Affected if VNC client applications like vncviewer, remmina, or vinagre are installed and may be used to connect to VNC servers
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Confirm library linkageRun 'ldd /usr/bin/vncviewer' or 'ldd $(which remmina)' to verify they link against libvncclient, then check that library version as shown in step 2Affected if The VNC client binary links to a libvncclient version < 0.9.12
A system is affected if it has a LibVNC client library version below 0.9.12 installed and runs VNC client software that uses this library to connect to potentially untrusted VNC servers.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor data0.9.12
Update LibVNC to the version containing commit c3115350eb8bb635d0fdb4dbbb0d0541f38ed19c or later. If patching is not possible, implement network-level controls to limit VNC connections to trusted servers and monitor for unusual client resource consumption.
Fix this in Ubuntu Linux
Scoped from the published advisory
- Consultation4.0 h
- Implementation8.0 h
- Testing6.0 h
- Review / QA3.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $5,888.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2018-20021 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2018-20021 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Version or environment caveats, and links to real fixes
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