Psono Server (CE & EE) versions 1.0.0 through 7.2.3 did not enforce the direction of file-transfer credentials on file-repository operations. An authenticated remote attacker with read-only access to a file could present a download transfer to the upload endpoint, obtain a signed upload URL for an attacker-selected object key, and append a chunk to the owner's file. Exploitation could upload or overwrite repository objects and consume storage, subject to transfer size, chunk-count, and lifetime limits.