I don't think that GLONASS, at least the military-grade stuff, can be hacked or spoofed, but since radio frequencies are well-known any adversary can just pump

I don't think that GLONASS, at least the military-grade stuff, can be hacked or spoofed, but since radio frequencies are well-known any adversary can just pump enough noise to make the system unusable. This vulnerability is not limited to GLONASS - any satellite positioning system is vulnerable to "pump too much noise and it's unreadable without space-grade stationary equipment", which is already demonstrated by Iran versus satellite television and radio.