i18next is a language translation framework. When using the .init method, passing interpolation options without passing an escapeValue will default to undefined rather than the assumed true. This can result in a cross-site scripting vulnerability because user input is assumed to be escaped, but is not. This vulnerability affects i18next 2.0.0 and later.

Affected: npm: i18next

Affected versions of `i18next` may fail to sanitize user input when certain configuration options are used. When using the `.init` method, passing interpolation options without passing an `escapeValue` will default to `undefined` rather than the assumed `true`.

## Proof of Concept

```js var init = i18n.init({ interpolation: { prefix: "__", suffix: "__", escapeValue: true } }, function(){ var test = i18n.t('__firstName__ __lastName__', { firstName: 'Bob', lastName: '["foo","bar"]', }); console.log(test); }); ``` When `escapeValue` is explicitly passed, the result of `test` is:

```html <script>alert(1)</script> Johnson ```

This is supposed to be the default. However, if `escapeValue` is not included, the result is the unescaped string: ```html <script>alert(1)</script> Johnson ```

## Recommendation

Update to version 3.4.4 or later.