Overview A heap-based buffer overflow exists in the Tight JPEG decoding component of the TightVNC Windows Viewer version 1.3.10 and affected UltraVNC Windows Viewers. An attacker controlling a malicious VNC server can trigger memory corruption by sending a specially crafted screen update. Successful exploitation can crash the viewer and may allow arbitrary code execution, although only denial of service conditions were demonstrated during testing. Description TightVNC and UltraVNC provide remote desktop access using the Remote Framebuffer (RFB) protocol. Their viewer applications connect to VNC servers and decode screen updates for local display. Tight encoding supports JPEG compression of i