Affected: Bitnami: rclone

rclone is a command-line program to sync files and directories to and from different cloud storage providers. From 1.70.0 until 1.75.1, the serve/start RC interface accepts per-server proxyOpt.AuthProxy settings, and the FTP and S3 constructors in cmd/serve/ftp/ftp.go and cmd/serve/s3/server.go incorrectly check the process-global proxy.Opt.AuthProxy value instead. When the global value is empty, the request-local authentication proxy is ignored: FTP falls back to the fixed filesystem with username anonymous and any password, while S3 with AuthKey serves the fixed RC fs rather than the backend selected by the proxy. The dedicated command-line servers that configure the global option are not affected. This issue is fixed in version 1.75.1.

rclone is a command-line program to sync files and directories to and from different cloud storage providers. From 1.70.0 until 1.75.1, the serve/start RC interface accepts per-server proxyOpt.AuthProxy settings, and the FTP and S3 constructors in cmd/serve/ftp/ftp.go and cmd/serve/s3/server.go incorrectly check the process-global proxy.Opt.AuthProxy value instead. When the global value is empty, the request-local authentication proxy is ignored: FTP falls back to the fixed filesystem with username anonymous and any password, while S3 with AuthKey serves the fixed RC fs rather than the backend selected by the proxy. The dedicated command-line servers that configure the global option are not affected. This issue is fixed in version 1.75.1.

Affected: Go: github.com/rclone/rclone

## Summary

`serve/start` accepts protocol options in a per-server `proxyOpt` object. The FTP and S3 RC adapters parse that object and pass it to their server constructors, but the constructors decide whether proxy authentication is enabled by checking the process-global `proxy.Opt.AuthProxy` instead of the supplied `proxyOpt.AuthProxy`.

When the process-global option is empty—the normal case when only the RC request configures the server—the supplied authentication proxy is silently ignored. FTP falls back to its fixed-backend mode, whose defaults accept username `anonymous` with any password, exposing read, write, and delete operations without the authentication the operator configured. S3 falls back to the fixed filesystem: with an `auth_key`, any holder of that key reaches the fixed RC `fs` instead of the backend selected by the auth proxy.

The S3 no-`auth_key` mode is explicitly documented as anonymous and is not part of this vulnerability claim. The confirmed S3 impact is proxy-based authorization/backend routing being ignored when S3 authentication is otherwise enabled.

Confirmed affected versions are `v1.70.0` through `v1.75.0`, plus development commit `5629f2668c69149bf3d9d8e2a25bb32a2648606e`. The dedicated CLI commands use the process-global option and are not affected by this configuration mismatch.

## Affected Assets & Attack Surface

- `cmd/serve/rc.go:68-93` documents nested per-server `proxyOpt` support, including `AuthProxy`. - `cmd/serve/rc.go:111-148`…

Affected: Ubuntu:18.04:LTS: rclone, Ubuntu:Pro:20.04:LTS: rclone, Ubuntu:Pro:22.04:LTS: rclone, Ubuntu:Pro:24.04:LTS: rclone, Ubuntu:Pro:26.04:LTS: rclone

rclone is a command-line program to sync files and directories to and from different cloud storage providers. From 1.70.0 until 1.75.1, the serve/start RC interface accepts per-server proxyOpt.AuthProxy settings, and the FTP and S3 constructors in cmd/serve/ftp/ftp.go and cmd/serve/s3/server.go incorrectly check the process-global proxy.Opt.AuthProxy value instead. When the global value is empty, the request-local authentication proxy is ignored: FTP falls back to the fixed filesystem with username anonymous and any password, while S3 with AuthKey serves the fixed RC fs rather than the backend selected by the proxy. The dedicated command-line servers that configure the global option are not affected. This issue is fixed in version 1.75.1.