Minosoft is an open-source, multi-version Minecraft Java Edition client written in Kotlin. Starting in commit f1ae30e2b046a490026a8413b075685deb795122, the CryptManager  encryption routine ( CryptManager.kt ) initializes its AES cipher using an initialization vector (IV) that is set equal to the secret key rather than to a sufficiently random value. Because the IV is not random and is derived directly from the key, the encryption is vulnerable to chosen-ciphertext/chosen-plaintext attacks: an attacker who can submit specific messages for encryption can recover the secret key. This affects all versions supporting Minecraft protocol 1.7 and later. No patched version is available, and no known workarounds are available.