Description Nimbus accepted the "uploadedJarLocation" argument of "submitTopology" / "submitTopologyWithOpts" as a server-side path and opened it directly, without checking that it referred to a file the caller had actually uploaded. The intended flow is that a client first calls "beginFileUpload", which returns a path inside the Nimbus inbox, and uploads the jar in chunks to that location; nothing bound submission to that flow, and the "uploaders" map populated by "beginFileUpload" was never consulted at submit time. An authenticated user with topology submission rights could therefore submit any path readable by the Nimbus daemon user as their topology jar. Nimbus copied the file into the topology's jar blob, and the blob ACL grants the submitting subject read access, so the contents could then be retrieved with the ordinary blob download RPCs. Candidate targets include the Nimbus Kerberos keytab, Thrift and UI TLS private keys, and "storm.yaml" with the ZooKeeper authentication payload. Possession of the Nimbus keytab turns an ordinary tenant into a cluster administrator. In a deployment configured as the documentation recommends, submission is available to every authenticated principal when "nimbus.users" is unset, so no elevated privilege is required. Mitigation Upgrade to 3.1.0, where the submitted location is canonicalised and must resolve inside the Nimbus inbox. Users who cannot upgrade immediately should restrict topology submission to trusted principals via "nimbus.users" or "nimbus.groups", and should treat any file readable by the Nimbus daemon user as potentially exposed to submitters: rotate the Nimbus keytab and any TLS private keys or ZooKeeper credentials reachable from that account. Local mode is unaffected. Credit Independently reported to the Apache Storm PMC by n0mi1k, with a proof of concept. Also found by the ASF using Claude agents to study the security of open-source projects, validated and reported by Apache Storm.