CVE-2020-37134Public exploitHinoki check available

Application crash via malformed server name

Published Feb 5, 2026 · Updated Feb 5, 2026

Denial of service in UltraVNC Viewer 1.2.4.0 allows local users to crash the application through the VNC Server connection dialog. Public evidence does not identify the responsible function or exact faulty operation; it establishes that submitting a 256-byte server-name string terminates vncviewer.exe. The attack requires interactive access to paste the payload and select Connect, and the bounded consequence is loss of the viewer process.

CVSS severity4.6
Medium
EPSS probability0.38%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkAvailable
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Summary

What happened

Denial of service in UltraVNC Viewer 1.2.4.0 allows local users to crash the application through the VNC Server connection dialog. Public evidence does not identify the responsible function or exact faulty operation; it establishes that submitting a 256-byte server-name string terminates vncviewer.exe. The attack requires interactive access to paste the payload and select Connect, and the bounded consequence is loss of the viewer process.

The record

CVE
CVE-2020-37134
Published
Feb 5, 2026
Updated
Feb 5, 2026
Vendor
UltraVNC Team
Product
UltraVNC Viewer
Classifications
CWE-770, T1499
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 5, 2026CVE publishedPublication date reported by the CVE source.
  2. Feb 5, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=1.2.4.0

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

UltraVNC Team · UltraVNC Viewerversion=1.2.4.0

Published CVSS scores

7.5VulnCheckCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
4.6VulnCheckCVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:A/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-770Allocation of Resources Without Limits or Throttling
T1499Endpoint Denial of Service

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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