This CVE exposes a path traversal in rclone's serve restic command, but the exploitable condition is narrower than a typical web-facing vulnerability. The traversal only becomes reachable when you publish a subdirectory of a backend credential that retains access to parent or sibling paths—meaning your credential configuration is the gate, not just the code.
The vulnerability was introduced in rclone 1.40.0 when subdirectory serving was added, and the WithRemote handler processes paths for GET, HEAD, POST, and DELETE operations without sanitizing ../ sequences. The 1.75.0 patch addresses the immediate traversal, but the deeper structural issue remains: rclone's credential model doesn't enforce or even signal when a served subdirectory is drawing from an over-privileged credential. If your credential can read mybucket/, serving mybucket/shared/folder still leaves that parent permission intact—and any future path-processing bug in the handler layer can escape the subdirectory boundary.
The advisory lists WebDAV, FTP, HTTP, Memory, and SFTP backends as affected. This multi-backend exposure creates an amplification risk: if your credential spans protocols (say, S3 plus SFTP), a path traversal in the REST handler can pivot across protocol boundaries while using the same credential. The blast radius isn't limited to the restic endpoint—it's every backend type that credential touches.
What you should check: First, verify whether any rclone serve restic instances are publishing subdirectories of backends. If so, examine whether those backend credentials are scoped to exactly the served path or retain broader access. The ideal state is a credential limited to the specific subdirectory being served—no parent or sibling access. Second, audit your deployment for any other serve commands that expose subdirectories, since the same handler pattern likely exists elsewhere. Finally, after patching to 1.75.0 or later, monitor for any unexpected path patterns in your access logs that might indicate the fix is incomplete—path canonicalization behavior differs across backends (HTTP vs SFTP vs WebDAV all resolve paths differently), so a narrow sanitization might leave edge cases unblocked for some backend types.