CVE-2026-128321: Tight JPEG decoding in TightVNC and UltraVNC viewers contains a heap-based buffer overflow vulnerability

Tight JPEG decoding in TightVNC and UltraVNC viewers contains a heap-based buffer overflow because an attacker-controlled framebuffer rectangle width is not validated against a fixed-size decoding buffer. A malicious VNC server can cause an out-of-bounds heap write when a user connects, resulting in application crash and potentially other memory-corruption impacts.