CVE-2020-25708: A divide by zero issue was found to occur in libvncserver-0.9.12

This week

HIGH 7.5REMOTEWATCHLISTDOWNGRADEMITIGATEMITIGATE

CVE-2020-25708 is a high-severity flaw (CVSS 7.5) affecting libvncserver, enterprise linux, debian linux. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

A divide by zero issue was found to occur in libvncserver-0.9.12. A malicious client could use this flaw to send a specially crafted message that, when processed by the VNC server, would lead to a floating point exception, resulting in a denial of service.

Why this priority

High severity
Public exploit reference
Remotely exploitable, no login, no user action
On your watchlist

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	1.6% (top 24%)
CISA exploited list	No
Weakness	CWE-369
Published	2020-11-27
Last modified	2026-06-17

Publisher (CNA): Red Hat, Inc. · Vendor: debian · libvncserver project · redhat

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2020-11-27 18:15 UTCPublished CVE record published
2026-06-17 03:07 UTCUpdated Record last modified

libvncserver project libvncserver DOWNGRADE

Affected: 0.9.12

Fixed in: no fixed release known

Safe to downgrade to: a release before 0.9.12

1. Check installed version

apt-cache policy libvncserver || rpm -q libvncserver || libvncserver --version

2. No fixed release: DOWNGRADE to a release before 0.9.12 (Debian / Ubuntu)

apt-cache madison libvncserver sudo apt install libvncserver=<VERSION_BEFORE_0.9.12> sudo apt-mark hold libvncserver

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list libvncserver sudo dnf downgrade libvncserver-<VERSION_BEFORE_0.9.12> sudo dnf versionlock add libvncserver

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

redhat enterprise linux MITIGATE

Affected: 6.0 · 7.0 · 8.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 6.0

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

debian debian linux MITIGATE

Affected: 10.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 10.0

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2020-25708?

libvncserver: downgrade or apply the listed mitigation; enterprise linux: mitigate or apply the listed mitigation; debian linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2020-25708 being exploited?

CVE-2020-25708 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2020-25708 affect?

CVE-2020-25708 affects libvncserver, enterprise linux, debian linux. Severity is high (CVSS 7.5). A divide by zero issue was found to occur in libvncserver-0.9.12. A malicious client could use this flaw to send a specially crafted message that, when processed by the VNC server, would lead to a floating point exception, resulting in a de

How urgent is CVE-2020-25708?

Priority 60/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action; On your watchlist

Software pages

Debian vulnerabilities

Related CVEs

CVE-2026-32854 HIGH 7.5 UPGRADE LibVNCServer versions 0.9.15 and prior (fixed in commit dc78dee) contain null pointer dereference vulnerabilit
CVE-2026-32853 HIGH 8.1 UPGRADE LibVNCServer versions 0.9.15 and prior (fixed in commit 009008e) contain a heap out-of-bounds read vulnerabili
CVE-2020-29260 HIGH 7.5 DOWNGRADE MITIGATE libvncclient v0.9.13 was discovered to contain a memory leak via the function rfbClientCleanup().
CVE-2020-14405 MEDIUM 6.5 UPGRADE MITIGATE An issue was discovered in LibVNCServer before 0.9.13
CVE-2020-14404 MEDIUM 5.4 UPGRADE MITIGATE An issue was discovered in LibVNCServer before 0.9.13

References

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