GHSA-945v-v9p3-v5xw: rclone local `--metadata` applies attacker-controlled mode/uid - setuid binary planted from an untrusted remote

When writing an object with metadata, the local backend applies the source-supplied mode, uid, and gid verbatim: it parses mode as an octal integer and passes it straight into os.Chmod(o.path, os.FileMode(umode)), and passes uid/gid straight into os.Chown. The value is never masked to permission bits, so any value with Go’s ModeSetuid (1«23) or ModeSetgid (1«22) bit set causes the setuid/setgid bit to be applied. Because both the file content and its metadata come from the (attacker-controlled) source remote, an attacker stores a binary of their choosing with mode = 40000755 (and uid = 0); when the victim runs rclone copy -M <remote>: /dest, rclone writes the attacker’s binary and makes it setuid. If the victim runs rclone as root (typical for system backup/restore), the uid=0 chown plus setuid produces a root-owned setuid binary with attacker content — any local user then escalates to root. When rclone runs as a non-root service user, the planted setuid binary is owned by that user, giving any local user that user’s privileges (lateral escalation / persistent backdoor).