Comcast is currently pushing SB_KOMODO-18.104.22.168 SCMO1-NOSH to SB6120, SB6121, and SB6141 modems on their network (it makes no difference whether the modem is leased or customer owned).
Until/unless Time Warner decides to push a newer firmware to your modem, you are going to be stuck with what you have. The DOCSIS standard generally does not allow the installation of firmware in a cable modem by the end user; it must be pushed by the ISP over the coax interface.
I have heard of some who have done it on some DOCSIS modems by opening the case and installing a JTAG interface on the modem's circuit board, but that is not a project for everyone. With that method, you would still need to obtain a copy of the firmware, and if your ISP did not support that firmware version, it would be almost immediately overwritten by their supported version as soon as the modem connected to their network anyway.--
We can never have enough of nature.
We need to witness our own limits transgressed, and some life pasturing freely where we never wander.