Hyperledger Indy Node is the server portion of a distributed ledger purpose-built for decentralized identity. In Hyperledger Indy before version 1.12.4, there is lack of signature verification on a specific transaction which enables an attacker to make certain unauthorized alterations to the ledger. Updating a DID with a nym transaction will be written to the ledger if neither ROLE or VERKEY are being changed, regardless of sender. A malicious DID with no particular role can ask an update for another DID (but cannot modify its verkey or role). This is bad because 1) Any DID can write a nym transaction to the ledger (i.e., any DID can spam the ledger with nym transactions), 2) Any DID can change any other DID's alias, 3) The update transaction modifies the ledger metadata associated with a DID.