session_by_x11_channel(int id)
{
	int i, j;

	for (i = 0; i < sessions_nalloc; i++) {
		Session *s = &sessions[i];

		if (s->x11_chanids == NULL || !s->used)
			continue;
		for (j = 0; s->x11_chanids[j] != -1; j++) {
			if (s->x11_chanids[j] == id) {
				debug("session_by_x11_channel: session %d "
				    "channel %d", s->self, id);
				return s;
			}
		}
	}
	debug("session_by_x11_channel: unknown channel %d", id);
	session_dump();
	return NULL;
}

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