Enumerating values from a linear congruential generator java Random()

Question

During my research on a java application, I discovered that the nextInt(64) function of the java.Random() class is used to generate the encryption key.

The key size is 16 bytes. I know that this generator is not recommended because it is vulnerable. Especially in this case, the value of each byte of the key is selected from a short range from 0x0 to 0x40.

I already got acquainted with the fact that it is possible to predict the next values ​​of the generator using the previous values. But in my case meyan has no data about the previous values (The key is encrypted and I don't have access to its values), so here we are talking about iterating over the key values. I don't understand how can I use the data that each next value depends on the previous one (oldseed parameter)?

protected int next(int bits) {
        long oldseed, nextseed;
        AtomicLong seed = this.seed;
        do {
            oldseed = seed.get();
            nextseed = (oldseed * multiplier + addend) & mask;
        } while (!seed.compareAndSet(oldseed, nextseed));
        return (int)(nextseed >>> (48 - bits));
}

How to reduce the number of enumeration for such a 16-byte key?