The end-of-life date for 2.5 version will occur on December 31 2018.
After that date no development, no security updates and no further bug fixes and vulnerability fixes will be provided on this firmware.
All systems will keep on working as well as customers with active maintenance will anyway continue to receive technical support, but for best practice we strongly recommend to carry out the upgrade to the newest available version at your earliest convenience.
The latest firmware currently available is 5.0, and it can be installed onto a 3.0 version, so please complete the migration from 2.5 to 3.0 first. https://help.endian.com/hc/en-us/articles/230741007-Migration-from-Version-3-0-to-5-0-
For all details about Endian End of Life Policies please refer to: https://help.endian.com/hc/en-us/articles/218147188-End-of-Life-Policy or email to firstname.lastname@example.org