Hypothetically, what could an attacker achieve if they have a copy of of
Nothing. The attacker already has it: it is distributed with the OpenSSH source code. This file is used to define the group in which the Diffie-Hellman key exchange may run; the group description is public, it contains no secret value, and can be shared at will. OpenSSH includes several group definitions and selects one at random just because they are paranoid (which is not necessarily a bad thing, for a security product).