GHSA-6457-mxpq-4fqq i18nextify has DOM XSS via javascript:/data: URL schemes in translated href/src attributes

• npm i18nextify: < 4.0.8 → fixed in 4.0.8

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,...` 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 ``, ``, or `` 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 `i18next.options.sanitize`. Defaults to pass-through to preserve existing behaviour for the main use case. Affected versions All versions of `i18nextify` prior to 4.0.8. Patch Fixed in 4.0.8. The URL-scheme blocklist is `^\s*(javascript|data|vbscript|file)\s*:` (case-insensitive) applied to each translated value before it is joined back into the `href`/`src` attribute. Values matching the blocklist are replaced with an empty string so the attribute becomes harmless rather than leaving the attacker's URL in place. Workarounds No workaround short of upgrading. If you cannot upgrade immediately, audit every translation file for `javascript:`, `data:`, `vbscript:`, and `file:` prefixes in any value that may reach an `href`/`src` position, and restrict translation-file write access to trusted operators. Serving translations over HTTPS and pinning the translation backend to an internal origin reduce the MITM surface. Credits Discovered via an internal security audit of the i18next ecosystem.