: Obtain cmterm-7975-sip.9-4-2SR4.zip from the Cisco Software Central.
If the phone logs show an "Authentication Failed" error, ensure that your ITL/CTL files are synced correctly. cmterm7975sip942sr4zip upd
Log into Cisco.com (with a valid SmartNet contract) and navigate to: Download the file named cmterm7975sip942sr4zip.upd . Do not unzip it manually yet. : Obtain cmterm-7975-sip
: Go to Cisco Unified Serviceability , navigate to Tools > Control Center - Feature Services , and restart the Cisco TFTP service to register the new files. cmterm7975sip942sr4zip upd
The update is a highly recommended "legacy-stable" firmware for the Cisco 7975G. It provides the necessary security patches to keep these aging but reliable devices functioning in modern network environments.
After the phones reboot (allow 5–10 minutes), verify success: