AES link encryption without MAC - what are the possible problems?

Question

Computer networks

There is a communication channel between two old computers (respectively, they are low-powered) via L2TP / IPsec, the AES-128-CBC algorithm is selected for encrypting the communication channel without authentication of MAC packets (without md5, sha1, sha256, etc.), how much is it safe ? As I understand it, packet authentication is only necessary so that before decrypting the AES algorithm, check whether the hackers have changed the packet, if everything is fine, then the decryption takes place and the packet is trusted. Let's say if there is no MAC and the hackers changed the package, then the package is decrypted and what they do with it next is not entirely clear to me, according to the idea, if you do not know the encryption key, then when the package is changed, there will be a hash or garbage after decryption.
Key exchange when establishing a connection via DH (Diffie-Hellman) and with authorization by RSA2048 keys, it is unrealistic to find out and intercept the encryption key.
I don't want to use MAC. the communication speed is already very low, and if you also add the signature of the packages, the speed will generally be below the plinth. Please do not offer to change the MTU size or change to AES-128-GCM encryption or change the communication channel encryption method.
Q : When using AES-128-CBC without MAC packet authentication, what are the possible problems?

Answer 1

there won't be any problems. The hashing algorithms you listed have been considered vulnerable for several years now.