Description "DefaultStateSerializer", used to persist and restore stateful bolt checkpoints, configured Kryo with class registration disabled and an instantiation strategy that constructs objects without invoking their constructors, then deserialized whatever bytes the state store returned. A party able to write to the topology's keyspace in the state store, for example a co-tenant of a shared Redis instance or anyone with network access to it, could therefore place a serialized object graph that executes code inside the worker JVM when the state is restored. This requires the Redis-backed state provider, which is not the default. Write access to a state-store key is a data-plane privilege; code execution in the worker JVM is not, so the two are not equivalent. Mitigation Upgrade to 3.1.0, where the state serializer requires registered classes. Note that this is a behaviour change for existing state: checkpoints written by an affected version may fail to restore, and a migration step may be required. Users who cannot upgrade immediately should restrict network and credential access to the state store to the cluster itself. Credit The ASF -- found using Claude agents to study the security of open-source projects, validated and reported by Apache Storm.