In freeradius, when an EAP-SIM supplicant sends an unknown SIM option, the server will try to look that option up in the internal dictionaries. This lookup will fail, but the SIM code will not check for that failure. Instead, it will dereference a NULL pointer, and cause the server to crash.
https://github.com/FreeRADIUS/freeradius-server/commit/f1cdbb33ec61c4a64a