Gstreamer1-plugins-bad-free: gstreamer: signed integer overflow in vmnc decoder cursor payload handling

A signed integer overflow vulnerability was found in GStreamer's VMnc decoder. A crafted VMnc stream with large cursor dimensions can overflow signed integer payload-size arithmetic, bypassing a length check and leading to out-of-bounds reads. A remote attacker could trick a user into opening a specially crafted VMnc file, potentially causing a crash or information disclosure.