rclone · Vulnerability

Rclone is a command-line program to sync files and directories to and from different cloud storage providers. Starting in version 1.48.0 and prior to version 1.73.5, the RC endpoint `operations/fsinfo` is exposed without `AuthRequired: true` and accepts attacker-controlled `fs` input. Because `rc.GetFs(...)` supports inline backend definitions, an unauthenticated attacker can instantiate an attacker-controlled backend on demand. For the WebDAV backend, `bearer_token_command` is executed during backend initialization, making single-request unauthenticated local command execution possible on reachable RC deployments without global HTTP authentication. Version 1.73.5 patches the issue.

Rclone is a command-line program to sync files and directories to and from different cloud storage providers. Starting in version 1.48.0 and prior to version 1.73.5, the RC endpoint `operations/fsinfo` is exposed without `AuthRequired: true` and accepts attacker-controlled `fs` input. Because `rc.GetFs(...)` supports inline backend definitions, an unauthenticated attacker can instantiate an attacker-controlled backend on demand. For the WebDAV backend, `bearer_token_command` is executed during backend initialization, making single-request unauthenticated local command execution possible on reachable RC deployments without global HTTP authentication. Version 1.73.5 patches the issue.

Rclone is a command-line program to sync files and directories to and from different cloud storage providers. Starting in version 1.48.0 and prior to version 1.73.5, the RC endpoint `operations/fsinfo` is exposed without `AuthRequired: true` and accepts attacker-controlled `fs` input. Because `rc.GetFs(...)` supports inline backend definitions, an unauthenticated attacker can instantiate an attacker-controlled backend on demand. For the WebDAV backend, `bearer_token_command` is executed during backend initialization, making single-request unauthenticated local command execution possible on reachable RC deployments without global HTTP authentication. Version 1.73.5 patches the issue.

### Summary The RC endpoint `operations/fsinfo` is exposed without `AuthRequired: true` and accepts attacker-controlled `fs` input. Because `rc.GetFs(...)` supports inline backend definitions, an unauthenticated attacker can instantiate an attacker-controlled backend on demand. For the WebDAV backend, `bearer_token_command` is executed during backend initialization, making single-request unauthenticated local command execution possible on reachable RC deployments without global HTTP authentication. ### Preconditions Preconditions for this vulnerability are: - The rclone remote control API **must** be enabled, either by the `--rc` flag or by running the `rclone rcd` server - The remote control API **must** be reachable by the attacker - by default rclone only serves the rc to localhost unless the `--rc-addr` flag is in use - The rc must have been deployed **without** global RC HTTP authentication - so not using `--rc-user`/`--rc-pass`/`--rc-htpasswd`/etc ### Details The root cause consists of the following pieces: 1. `operations/fsinfo` is not protected with `AuthRequired: true` 2. `operations/fsinfo` calls `rc.GetFs(...)` on attacker-controlled input 3. `rc.GetFs(...)` supports inline backend creation through object-valued `fs` 4. WebDAV backend initialization executes `bearer_token_command` Relevant code paths: - [`fs/operations/rc.go`](https://github.com/rclone/rclone/blob/bf55d5e6d37fd86164a87782191f9e1ffcaafa82/fs/operations/rc.go) - `operations/fsinfo` is registered without `AuthRequired: true` - `rcFsInfo()` calls `rc.GetFs(ctx, in)` - [`fs/rc/cache.go`](https://github.com/rclone/rclone/blob/bf55d5e6d37fd86164a87782191f9e1ffcaafa82/fs/rc/cache.go) - `GetFs()` / `GetFsNamed()` can parse an object-valued `fs` - `getConfigMap()` converts attacker-controlled JSON into a backend config string - [`backend/webdav/webdav.go`](https://github.com/rclone/rclone/blob/bf55d5e6d37fd86164a87782191f9e1ffcaafa82/backend/webdav/webdav.go) - `bearer_token_command` is a supported backend option - `NewFs(...)` calls `fetchAndSetBearerToken()` when `bearer_token_command` is set - `fetchBearerToken()` invokes `exec.Command(...)` This creates a practical single-request unauthenticated command-execution primitive on reachable RC servers without global HTTP authentication. This was alidated on: - current `master` as of 2026-04-14: `bf55d5e6d37fd86164a87782191f9e1ffcaafa82` - latest public release tested locally: `v1.73.4` This was also validated on a public amd64 Ubuntu host controlled by the tester, using direct host execution (not containerized PoC execution). ### PoC #### Minimal single-request form PoC Start a vulnerable RC server: ```bash rclone rcd --rc-addr 127.0.0.1:5572 ``` No `--rc-user`, no `--rc-pass`, no `--rc-htpasswd`. Then send a single request: ```bash curl -sS -X POST http://127.0.0.1:5572/operations/fsinfo \ --data-urlencode "fs=:webdav,url='http://127.0.0.1/',vendor=other,bearer_token_command='/usr/bin/touch /tmp/rclone_fsinfo_rce_poc_marker':" ``` Expected result: - HTTP 200 JSON response from `operations/fsinfo` - `/tmp/rclone_fsinfo_rce_poc_marker` is created on the host ### Impact This is effectively a single-request unauthenticated command-execution vulnerability on reachable RC deployments without global HTTP authentication. In practice, command execution in the rclone process context can lead to higher-impact outcomes such as local file read, file write, or shell access, depending on the deployed environment. #### Testing performed This was successfully reproduced: - on a local test environment - on a public amd64 Ubuntu host controlled by the tester On the public host it was confirmed: - the unauthenticated `operations/fsinfo` exploit worked - command execution occurred on the host - the issue was reproducible through direct host execution

The operations/fsinfo remote control (RC) endpoint in rclone was registered without requiring authentication. This allowed unauthenticated callers to instantiate arbitrary backends via inline backend definitions, which could lead to local command execution if the backend configuration allows it (e.g., via bearer_token_command in webdav or ssh in sftp).