dbcve.org
Ubuntu LinuxOperating system · Canonical

CVE-2018-20024

HIGH · 7.5 CVSS v3.0 Published 2018-12-19
Fix available
A fix is available. Upgrade to 0.9.12 or later.
See remediation →
84/100
Remediation priority · High
Remotely reachable No privileges Zero-click

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 · unedited
LibVNC before commit 4a21bbd097ef7c44bb000c3bd0907f96a10e4ce7 contains null pointer dereference in VNC client code that can result DoS.

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 confidence

LibVNC contains a null pointer dereference vulnerability in the VNC client code that can be exploited to cause a Denial of Service. The vulnerability exists in versions of LibVNC prior to commit 4a21bbd097ef7c44bb000c3bd0907f96a10e4ce7. When processing certain VNC server responses or handling client connections, the code fails to properly validate a pointer before dereferencing it, leading to a crash.

MitigationUpdate LibVNC to version containing commit 4a21bbd097ef7c44bb000c3bd0907f96a10e4ce7 or later. If patching is not feasible, implement network-level filtering and rate limiting for VNC connections as a compensating control.

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
Affected:= 14.04= 16.04= 18.04= 18.10
Debian LinuxOperating system
Affected:= 8.0= 9.0
LibvncserverApplication
Affected:< 0.9.12

CVSS 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 checks

Work through these to decide whether this CVE applies to you.

  1. Identify if Libvncserver is installed
    On Debian/Ubuntu, run: dpkg -l | grep -i libvnc or check for library files with: find /usr -name '*libvnc*' 2>/dev/null
    Affected if No Libvncserver packages or libraries are found, the system is not affected by this specific vulnerability
  2. Determine installed Libvncserver version on Ubuntu
    Run: dpkg -l libvncserver0 or apt-cache policy libvncserver0
    Affected if The installed version is lower than the version shipped in the affected Ubuntu releases (14.04, 16.04, 18.04, 18.10)
  3. Determine installed Libvncserver version on Debian
    Run: dpkg -l libvncclient0 or apt-cache policy libvncclient0
    Affected if The installed version is lower than the version present in Debian 8.0 or 9.0 repositories
  4. Check Libvncserver library version directly
    Run: ldconfig -p | grep vnc and then check the library file version with: strings /path/to/libvncserver.so.X | grep -i version 2>/dev/null
    Affected if The library version is 0.9.12 or lower, or the library predates commit 4a21bbd097ef7c44bb000c3bd0907f96a10e4ce7
  5. Verify if VNC client functionality is in use
    Check running processes that may use LibVNC: ps aux | grep -i vnc or check for VNC-related services: systemctl list-units --type=service | grep -i vnc
    Affected if VNC client services or applications linked to LibVNC are actively running, exposing the vulnerability to malicious VNC server responses

A system is affected if it has any version of Libvncserver installed that is older than 0.9.12, or any version shipped with Ubuntu 14.04/16.04/18.04/18.10 or Debian 8.0/9.0, especially when VNC client functionality is actively used.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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 data
Upgrade available Upgrade to 0.9.12 or later
Fixed in 0.9.12
Interim mitigation

Update LibVNC to version containing commit 4a21bbd097ef7c44bb000c3bd0907f96a10e4ce7 or later. If patching is not feasible, implement network-level filtering and rate limiting for VNC connections as a compensating control.

Fix this in Ubuntu Linux Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing6.0 h
  • Review / QA3.0 h
15.0 hours of engineering $2,560
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $4,096.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2018-20024 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.

Get it on GitHub Scan in the browser

References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2018-20024 in production — separate from our analysis above.

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data