client_x11_display_valid(const char *display)
{
	size_t i, dlen;

	dlen = strlen(display);
	for (i = 0; i < dlen; i++) {
		if (!isalnum((u_char)display[i]) &&
		    strchr(SSH_X11_VALID_DISPLAY_CHARS, display[i]) == NULL) {
			debug("Invalid character '%c' in DISPLAY", display[i]);
			return 0;
		}
	}
 	return 1;
 }

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