Executive brief
A security flaw in rclone's restic server mode allows one user to access another user's private backup files. Rclone is a tool used to manage and sync files across different storage providers. In multi-tenant setups where multiple users share the same server, an authenticated user can bypass isolation controls to read, modify, or delete the backup data of other customers.
Technical details
An authorization bypass exists in `cmd/serve/restic/restic.go` when the `--private-repos` flag is used. The vulnerability is caused by a path desynchronization between two middlewares: `checkPrivate` validates the user based on a routed path segment, while `WithRemote` extracts the backend object path from the raw, uncanonicalized URL. By using path traversal sequences (e.g., `/me/../victim/`), an authenticated attacker can satisfy the authorization check for their own namespace while the backend resolves the final path to a different user's repository. This affects backends that perform POSIX-style path cleaning, such as SFTP, FTP, and the internal memory backend. The issue is addressed in version 1.74.4.
Affected products
- rclone rclone <= 1.74.3
Timeline
- 2026-07-08: disclosed
- 2026-08-05: advisory