Denial of Service Vulnerability in UltraVNC Viewer by UltraVNC
CVE-2019-25600

7.1HIGH

Key Information:

Vendor

Uvnc

Status
Ultravnc Viewer
Vendor
CVE Published:
22 March 2026

Badges

👾 Exploit Exists🟡 Public PoC

What is CVE-2019-25600?

UltraVNC Viewer version 1.2.2.4 is vulnerable to a denial of service attack, which occurs when an attacker inputs an oversized string of characters into the VNC Server input field. Specifically, by pasting a malicious string composed of 256 identical characters and then clicking 'Connect', the application can be forced to crash due to a buffer overflow condition. This vulnerability can disrupt the functionality of the viewer, making it critical for users to remain aware and implement necessary updates.

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Affected Version(s)

UltraVNC Viewer 1.2.2.4

Exploit Proof of Concept (PoC)

PoC code is written by security researchers to demonstrate the vulnerability can be exploited. PoC code is also a key component for weaponization which could lead to ransomware.

CVE-2019-25600 - Proof of Concept

References

https://www.exploit-db.com/exploits/46702
exploit
https://www.uvnc.com/
product
https://www.uvnc.com/downloads/ultravnc/126-download-ultr...
product

CVSS V4

Score:
7.1
Severity:
HIGH
Confidentiality:
None
Integrity:
None
Availability:
High
Attack Vector:
Network
Attack Complexity:
Low
Attack Required:
None
Privileges Required:
Undefined
User Interaction:
Unknown

Timeline

  • 🟡

    Public PoC available

  • 👾

    Exploit known to exist

  • Vulnerability published

  • Vulnerability Reserved

Credit

Victor Mondragón
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