Ultravnc
CVE-2020-37133
HIGH
Vulnerability Assessment
| Weakness |
CWE
OWASP Top 10:2025
A06:2021 - Vulnerable and Outdated Components
ASVS 5.0
V15 - Secure Coding and Architecture Stack buffer bounds checking
MITRE ATT&CK
1 technique across 1 tactic: Execution The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up. |
| Impact | CVSS 7.5 (HIGH). Attack vector: Network. Complexity: Low. Privileges required: None. User interaction: None. Public exploit/POC available. |
| Exploit ScenarioDerived | An attacker could exploit this vulnerability to crash the application. |
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Alert meAnalysisAIv1 – Mar 12, 2026
UltraVNC Launcher 1.2.4.0 contains a denial of service vulnerability in the Repeater Host configuration field that allows attackers to crash the application. Attackers can paste an overly long string of 300 characters into the Repeater Host property to trigger an application crash. [CVSS 7.5 HIGH]
RemediationAI
Monitor vendor advisories for a patch. Restrict network access to the affected service where possible.
Affects your stack
Find out whether the stacks and servers you run are on an affected version.
Checking this CVE against your own stacks and servers is part of the Basic plan and up.
Technical ContextAI · show details
Classified as CWE-121 (Stack-based Buffer Overflow). Affects Ultravnc. UltraVNC Launcher 1.2.4.0 contains a denial of service vulnerability in the Repeater Host configuration field that allows attackers to crash the application. Attackers can paste an overly long string of 300 characters into the Repeater Host property to trigger an application crash.
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- Exploit and PoC references, threat intelligence from 22 sources
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Severity by source
AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Primary rating from NVD · only source for this CVE.
CVSS VectorNVD
Lifecycle Timeline
2DescriptionCVE.org
UltraVNC Launcher 1.2.4.0 contains a denial of service vulnerability in the Repeater Host configuration field that allows attackers to crash the application. Attackers can paste an overly long string of 300 characters into the Repeater Host property to trigger an application crash.
Executive ViewAI
UltraVNC Launcher 1.2.4.0 is vulnerable to a denial of service attack that can crash the application when users input excessively long strings into the Repeater Host configuration field. Organizations using this software for remote access operations face potential service interruptions if attackers exploit this vulnerability, though data breach risk is minimal.
Restrict administrative access to UltraVNC Launcher configuration interfaces through network segmentation and role-based access controls. Disable or restrict the Repeater Host feature if not required for operations. Implement input validation at the application level if configurable. Monitor application logs for unexpected crashes and implement endpoint detection and response (EDR) to alert on process termination anomalies. Require administrator approval for configuration changes. Consider deploying application whitelisting to prevent unauthorized execution of UltraVNC components.
Threat Intelligence Overview
NVD
CVE.org
EPSS
Exploit-DB
How this decision was reached
The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.
What every action level means
SSVC AssessmentENISA
Priority Score
Attack Technique
Denial of Service attacks render applications or systems unavailable by overwhelming resources or triggering failure conditions.
Affected Products (CPE)CVE.org
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UltraVNC revision 1211 has multiple improper null termination vulnerabilities in VNC server code, which result in out-of
UltraVNC revision 1211 has a heap buffer overflow vulnerability in VNC server code inside file transfer offer handler, w
UltraVNC revision 1211 has a heap buffer overflow vulnerability in VNC server code inside file transfer request handler,
UltraVNC revision 1211 has multiple off-by-one vulnerabilities in VNC server code, which can potentially result in code
UltraVNC revision 1211 has a heap buffer overflow vulnerability in VNC server code inside file transfer handler, which c
UltraVNC revision 1206 has multiple off-by-one vulnerabilities in VNC client code connected with improper usage of Clien
UltraVNC revision 1207 has multiple out-of-bounds access vulnerabilities connected with improper usage of ClientConnecti
UltraVNC revision 1207 has multiple out-of-bounds access vulnerabilities connected with improper usage of SETPIXELS macr
UltraVNC revision 1203 has out-of-bounds access vulnerability in VNC client inside Ultra2 decoder, which can potentially
GitHub PoC