static void vnc_refresh(DisplayChangeListener *dcl)
{
    VncDisplay *vd = container_of(dcl, VncDisplay, dcl);
    VncState *vs, *vn;
    int has_dirty, rects = 0;

    graphic_hw_update(NULL);

    if (vnc_trylock_display(vd)) {
        update_displaychangelistener(&vd->dcl, VNC_REFRESH_INTERVAL_BASE);
        return;
    }

    has_dirty = vnc_refresh_server_surface(vd);
    vnc_unlock_display(vd);

    QTAILQ_FOREACH_SAFE(vs, &vd->clients, next, vn) {
        rects += vnc_update_client(vs, has_dirty, false);
        /* vs might be free()ed here */
    }

    if (QTAILQ_EMPTY(&vd->clients)) {
        update_displaychangelistener(&vd->dcl, VNC_REFRESH_INTERVAL_MAX);
        return;
    }

    if (has_dirty && rects) {
        vd->dcl.update_interval /= 2;
        if (vd->dcl.update_interval < VNC_REFRESH_INTERVAL_BASE) {
            vd->dcl.update_interval = VNC_REFRESH_INTERVAL_BASE;
        }
    } else {
        vd->dcl.update_interval += VNC_REFRESH_INTERVAL_INC;
        if (vd->dcl.update_interval > VNC_REFRESH_INTERVAL_MAX) {
            vd->dcl.update_interval = VNC_REFRESH_INTERVAL_MAX;
        }
    }
}

This category addresses vulnerabilities caused by flawed access control mechanisms, where incorrect permission settings allow unauthorized users to access restricted resources.