The isolation seems mostly defined by this SELinux policy: https://github.com/android/platform_system_core/blob/lollipo...

   service media /system/bin/mediaserver
       class main
       user media
       group audio camera inet net_bt net_bt_admin net_bw_acct drmrpc mediadrm
       ioprio rt 4

You'd need another exploit to elevate from SELinux (and I think send MSSes for a self-propagating worm). Though given Android's abysmal patching, most Android kernels are also terribly outdated...