i18nextify has DOM XSS via javascript:/data: URL schemes in translated href/src attributes

Summary

Versions of i18nextify prior to 4.0.8 substitute {{key}} interpolation tokens inside src and href attribute values with the raw string returned by i18next.t(). The substitution logic in src/localize.js (replaceInside handler around line 122) only guards against a duplicated http:// origin prefix — it does not validate the URL scheme of the substituted value. A translated value such as javascript:alert(1) or data:text/html,<script>...</script> is applied unchanged to the live DOM attribute.

Impact

When an attacker can influence the content of a translation file or the translation-backend response — compromised translation CDN, user-contributed locales, MITM on a plain-HTTP backend, write access to the translation JSON — they can:

• Set any href on an anchor to a javascript: URI, executing arbitrary JavaScript when the victim clicks the link.
• Set any src on <iframe>, <object>, or <embed> to a data:text/html URI containing a full script payload that runs in the page's origin.
• Use vbscript: on legacy IE installations or file: for local-resource navigation attacks.

This path is distinct from the general i18nextify design that intentionally renders HTML from translations — href/src schemes are narrow and attack-specific, and no legitimate translation needs javascript: or data:. The fix therefore blocks these schemes outright without changing other behaviour.

Also fixed in 4.0.8

• debug / saveMissing URL-parameter substring match. The previous detection window.location.search.indexOf('debug=true') > -1 matched the substring anywhere in the query string. A URL like ?nosaveMissing=true silently enabled saveMissing mode, causing the victim's browser to POST every unknown translation key to the configured addPath — a form of CSRF-style abuse of missing-key reporting. ?track_debug=true enabled verbose debug logging, leaking i18next internals to the console. Now uses URLSearchParams for exact parameter matching.
• Optional sanitize(html, ctx) hook. The library's core purpose is to render HTML from translations — a behaviour that is safe only when the translation source is fully trusted. Applications with partially-trusted sources (user-contributed locales, third-party CDN, MITM-exposed HTTP backend) can now wire a sanitizer (e.g. DOMPurify) via . Defaults to pass-through to preserve existing behaviour for the main use case.