Summary A low-privilege MCP token holder with knowledge of an attachment path could read any file in shared storage, including attachments belonging to other bases and workspaces, because the MCP "readAttachment" tool did not verify the file's ownership. Details The MCP "readAttachment" tool accepts caller-supplied "path"/"url" values and streams the file via the storage adapter. The handler now looks up the path in "nc_file_references" and requires a non-deleted row whose "base_id" matches the caller's MCP context before streaming; otherwise it returns "Attachment is not accessible from this MCP context". The lookup tolerates both "download/uploads/..." and "uploads/..." styles. Impact Arbitrary read against shared storage scoped to attachments the caller's MCP context should not see. Exploitation requires an MCP token and a known attachment path. Credit This issue was reported by "@helwor-01" (https://github.com/helwor-01).