Pydio Cells 5.0.0 to 5.0.2 - Missing Authorization on the Share Link REST Handler

Summary

Pydio Cells 5.0.0 through 5.0.2 returns share-link details to any authenticated user. The REST handler for GET /a/share/link/{Uuid} in idm/share/rest/handler.go reads the workspace UUID from the path, calls LinkById, and writes the result with no authorization step, whereas the sibling handler for GET /a/share/cell/{Uuid} loads the workspace and requires MatchPolicies with ResourcePolicyAction_READ, returning a not-found error so that existence is not disclosed. Nothing compensates further down: GetLinkWorkspace reaches GetOrCreateWorkspace, which issues SearchWorkspace with a query carrying no ResourcePolicyQuery, and PrepareResourcePolicyQuery returns the query unmodified when that field is nil, so the workspace service applies no policy filter. The workspace UUID is not secret, because the unauthenticated public page served for a share link embeds it as START_REPOSITORY. Any account holding a standard user role can therefore submit the UUID and receive the link hash and URL, the owner's user identifier, the hidden share user login, the permission set, the download limit and count, the target users, the expiry, and the password-required flag, while a direct read of the shared node from the same account is refused.