Remote code execution in Indy's NODE_UPGRADE transaction

Indy Node is the server portion of a distributed ledger purpose-built for decentralized identity. In versions 1.12.4 and prior, the `pool-upgrade` request handler in Indy-Node allows an improperly authenticated attacker to remotely execute code on nodes within the network. The `pool-upgrade` request handler in Indy-Node 1.12.5 has been updated to properly authenticate pool-upgrade transactions before any processing is performed by the request handler. The transactions are further sanitized to prevent remote code execution. As a workaround, endorsers should not create DIDs for untrusted users. A vulnerable ledger should configure `auth_rules` to prevent new DIDs from being written to the ledger until the network can be upgraded.