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.

Psono Server versions 5.3.5 through 7.2.3 used a permission class that did not enforce token write scope when claiming a device code. An authenticated remote attacker holding a restricted API key-derived session could claim an attacker-controlled device code and obtain a full read-write session valid for up to 365 days, bypassing the original token's scope and lifetime restrictions. This did not bypass two-factor authentication or directly disclose plaintext secrets.