CVE-2019-25600 UltraVNC Viewer 1.2.2.4 Denial of Service via Buffer Overflow
Attackers can crash UltraVNC Viewer by pasting an oversized string into the server field, causing a buffer overflow.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- None listed
What is CVE-2019-25600?
CVE-2019-25600 is a high-severity memory corruption vulnerability in Uvnc UltraVNC Viewer, published on 22 Mar 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
UltraVNC Viewer 1.2.2.4 contains a denial of service vulnerability that allows attackers to crash the application by supplying an oversized string to the VNC Server input field. Attackers can paste a malicious string containing 256 repeated characters into the VNC Server field and click Connect to trigger a buffer overflow that crashes the viewer.
Weakness: CWE-787
Which versions are affected by CVE-2019-25600?
How do I fix CVE-2019-25600?
No fix has been published for CVE-2019-25600 yet. Limit exposure of the affected software until one is available.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2019-25600 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2019-25600 exists.
Sources
Also known as GHSA-6w7v-w6gw-pm7w.