CVE-2020-37134 UltraVNC Viewer 1.2.4.0 - 'VNCServer' Denial of Service
Attackers can crash UltraVNC Viewer by pasting a malformed payload into the VNC Server connection dialog, causing a denial of service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- A user has to click or open something
- Fix
- None listed
What is CVE-2020-37134?
CVE-2020-37134 is a medium-severity denial of service vulnerability in UltraVNC Viewer, published on 5 Feb 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Official description
UltraVNC Viewer 1.2.4.0 contains a denial of service vulnerability that allows attackers to crash the application by manipulating VNC Server input. Attackers can generate a malformed 256-byte payload and paste it into the VNC Server connection dialog to trigger an application crash.
Weakness: CWE-770
Which versions are affected by CVE-2020-37134?
How do I fix CVE-2020-37134?
No fix has been published for CVE-2020-37134 yet. Limit exposure of the affected software until one is available.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2020-37134 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2020-37134 exists.
Sources
Also known as GHSA-w28g-7hwj-hqwj.