ALTEr attack exploits the fact that LTE user data is encrypted in counter mode (AES-CTR) but not integrity protected, which allows us to modify the message payload. The current 5G specification does not require this security feature as mandatory, but leaves it as an optional configuration parameter. The attack is dangerous, but it is difficult to perform in real-world scenarios. The team said that the attacks are restricted to only 4G networks, as well as 5G networks.
Source: https://thehackernews.com/2018/06/4g-lte-network-hacking.html