Quick answers
- Is CVE-2026-128321 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-128321 being exploited in the wild.
- How severe is CVE-2026-128321?
- Informational severity, published 13 November 2026.
- Which products and versions are affected?
- TightVNC TightVNC Viewer; UltraVNC UltraVNC Viewer.
- Is there a fix for CVE-2026-128321?
- No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
- How is CVE-2026-128321 attacked?
- It is attacked over the network, in a web application.
- Am I affected by CVE-2026-128321?
- Check whether you run TightVNC Viewer or UltraVNC Viewer. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
Technical details
An attacker-controlled framebuffer rectangle width is not validated against a fixed-size decoding buffer in the Tight JPEG decoding component, leading to a heap-based buffer overflow. A malicious VNC server can trigger out-of-bounds heap writes when a user connects to it, potentially causing application crash or other memory corruption impacts. The vulnerability affects both TightVNC and UltraVNC viewers.
Affected products
- TightVNC TightVNC Viewer
- UltraVNC UltraVNC Viewer
Timeline
- 2026-11-13: disclosed