{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "locize"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "4.0.21"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [],
  "database_specific": {
    "cwe_ids": [
      "CWE-79",
      "CWE-346"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-04-22T20:32:11Z",
    "nvd_published_at": null,
    "severity": "HIGH"
  },
  "details": "### Summary\n\nVersions of the `locize` client SDK (the browser module that wires up the locize InContext translation editor) prior to 4.0.21 register a `window.addEventListener(\"message\", \u2026)` handler that dispatches to registered internal handlers (`editKey`, `commitKey`, `commitKeys`, `isLocizeEnabled`, `requestInitialize`, \u2026) **without validating `event.origin`**.\n\nThe pre-patch listener in `src/api/postMessage.js` gates dispatch on `event.data.sender === \"i18next-editor-frame\"` \u2014 that value sits inside the attacker-controlled message payload, not the browser-enforced origin. Any web page that could embed or be embedded by a locize-enabled host \u2014 an iframe on a third-party page, a `window.open`-ed victim, a parent frame reaching down \u2014 could send a crafted `postMessage` and trigger the internal handlers.\n\n### Impact\n\nDepending on which handler the attacker invokes, distinct consequences follow. All of them share the same root cause: the handlers implicitly assumed the payload came from the real editor iframe.\n\n- **Cross-origin DOM XSS** via `editKey` / `commitKeys`: the pre-patch `handleEditKey` assigned attacker-controlled payload values to `item.node.innerHTML` and to `item.node.setAttribute(attr, value)`. That allowed planting `\u003cscript\u003e`, `\u003cimg onerror\u003e`, or `onclick`/`onload`/`onfocus` event handlers; and on attribute writes, `href=\"javascript:\u2026\"` / `src=\"data:text/html,\u003cscript\u003e\u2026\"` / `style=\"\u2026\"` / etc.\n\n- **`api.source` / `api.origin` hijack** via `isLocizeEnabled`: the handler set `api.source = e.source; api.origin = e.origin` \u2014 attacker-controlled values. All subsequent `sendMessage` calls (which post translations, callbacks, etc., back toward `api.source`) would go to the attacker window rather than the real editor, leaking translation content and any metadata the SDK forwards.\n\n- **CSS-injection / layout-escape** via `requestPopupChanges`: `containerStyle.height` / `.width` were interpolated into `calc()` expressions and `popup.style.setProperty()` without validation, allowing attackers to inject additional CSS declarations (semicolons, `behavior:url()` on legacy IE, CSS-exfil patterns) into the popup inline style.\n\nExploitation requires the attacker-owned page to share a window reference with the locize-enabled host: typical vectors are an `iframe` on an attacker-controlled page, a `window.opener`/`window.open` relationship, or a parent frame that can `postMessage` into an embedded locize host. The SDK intended model is that only the editor iframe at `https://incontext.locize.app` (or the configured staging/development origin) can reach these handlers.\n\n### Affected versions\n\nAll versions of `locize` prior to **4.0.21**.\n\n### Patch\n\nFixed in **4.0.21**. Two layers:\n\n1. **Primary** \u2014 validate `event.origin` at the top of `window.addEventListener(\"message\", \u2026)` in `src/api/postMessage.js`. The expected origin is the configured iframe origin (`getIframeUrl()`), so custom environments continue to work. Messages from any other origin are silently dropped before any handler runs.\n\n2. **Defence-in-depth** \u2014 `handleEditKey` now rejects dangerous attribute-name writes (`on*`, `style`) and `javascript:` / `data:` / `vbscript:` / `file:` URLs on `href` / `src` / `action` / `formaction` / `xlink:href`; `innerHTML` assignments are sanitised through a throwaway DOMParser document (stripping `\u003cscript\u003e`, `\u003ciframe\u003e`, `\u003cobject\u003e`, `\u003cembed\u003e`, `\u003clink\u003e`, `\u003cmeta\u003e`, `\u003cbase\u003e`, `\u003cstyle\u003e` plus event handlers and dangerous URL schemes). Legitimate translation formatting (`\u003cb\u003e`, `\u003cem\u003e`, `\u003cstrong\u003e`, `\u003ca href=\"https://\u2026\"\u003e`, etc.) passes through.\n\n3. **CSS-injection** \u2014 `handleRequestPopupChanges` now requires `containerStyle.height` / `.width` to match a strict CSS length pattern; malformed values are dropped silently.\n\n### Workarounds\n\nNo workaround short of upgrading.\n\n### Credits\n\nDiscovered via an internal security audit of the locize ecosystem.",
  "id": "GHSA-w937-fg2h-xhq2",
  "modified": "2026-04-22T20:32:11Z",
  "published": "2026-04-22T20:32:11Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/locize/locize/security/advisories/GHSA-w937-fg2h-xhq2"
    },
    {
      "type": "WEB",
      "url": "https://github.com/locize/locize/commit/d006b75fadb8e8ab77b023e462850fc6e9170735"
    },
    {
      "type": "WEB",
      "url": "https://developer.mozilla.org/en-US/docs/Web/API/Window/postMessage#security_concerns"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/locize/locize"
    },
    {
      "type": "WEB",
      "url": "https://github.com/locize/locize/releases/tag/v4.0.21"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:H/A:L",
      "type": "CVSS_V3"
    }
  ],
  "summary": "locize Client SDK: Cross-origin DOM XSS \u0026 Handler Hijack Through Missing e.origin Validation in InContext Editor "
}