The implementation of EdDSA in EdDSA-Java (aka ed25519-java) through 0.3.0 exhibits signature malleability and does not satisfy the SUF-CMA (Strong Existential Unforgeability under Chosen Message Attacks) property. This allows attackers to create new valid signatures different from previous signatures for a known message.
https://github.com/str4d/ed25519-java/issues/82#issue-727629226