CVE-2019-25600Public exploitNetwork attack vector

Application crash via oversized server input

Published Mar 22, 2026 · Updated Mar 22, 2026

Out-of-bounds write in UltraVNC Viewer 1.2.2.4 allows attackers to crash the viewer through an oversized VNC Server field value. The VNC Server input handler fails to bound a 256-character repeated string before writing the value past the destination buffer. Exploitation requires user interaction to paste the string and select Connect; the demonstrated consequence is termination of the viewer process, not server interruption.

CVSS severity7.1
High
EPSS probability0.69%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Out-of-bounds write in UltraVNC Viewer 1.2.2.4 allows attackers to crash the viewer through an oversized VNC Server field value. The VNC Server input handler fails to bound a 256-character repeated string before writing the value past the destination buffer. Exploitation requires user interaction to paste the string and select Connect; the demonstrated consequence is termination of the viewer process, not server interruption.

The record

CVE
CVE-2019-25600
Published
Mar 22, 2026
Updated
Mar 22, 2026
Vendor
UltraVNC Team
Product
UltraVNC Viewer
Classifications
CWE-787, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 22, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 22, 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=1.2.2.4

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

UltraVNC Team · UltraVNC Viewerversion=1.2.2.4

Published CVSS scores

7.1VulnCheckCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
6.5VulnCheckCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H

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.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-787Out-of-bounds Write
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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