mathlive's Lack of Escaping of HTML allows for XSS

### Summary Despite the 0.104.0 patch escaping attribute-bearing constructs (`\htmlData`, `\href`), text-content reflection was missed. The `\text{}`, `\mbox{}` commands accept arbitrary characters in their body and emit them raw and unescaped into both the HTML markup and the MathML output, leading to XSS. ### Details `Box.toMarkup` at `src/core/box.ts:356` concatenates `this.value` into the rendered span without HTML-escaping. In text mode any literal character (`<`, `>`, `&`, `"`) is wrapped into a `TextAtom` whose `value` is the raw codepoint and lands in the markup unchanged. The MathML serializer at `src/formats/atom-to-math-ml.ts` is independently broken: `xmlEscape` deliberately omits the `&` rule, and `scanText`, `case 'text'`, and the `mode === 'text'` early return all emit `atom.value` raw. Both outputs flow into `innerHTML` sinks via the public API. `<math-span>` / `<math-div>` (`src/public/math-static-elements.ts:331,407`) bypass `MathfieldElement.createHTML` entirely. The editor and SSR paths route through `createHTML`, but its default value is the identity function (`src/public/mathfield-element.ts:789`). ### PoC 1. Go to https://mathlive.io/mathfield/demo/ 2. open DevTools console and paste: ```js const s = document.createElement('math-span'); s.style.display = 'block'; s.textContent = '\\text{<img src=x onerror=alert(1)>}'; document.body.appendChild(s); s.scrollIntoView(); ``` Equivalent payloads: `\mbox{<img src=x onerror=alert(1)>}` or ```js import { convertLatexToMarkup } from 'mathlive'; document.body.innerHTML = convertLatexToMarkup('\\text{<img src=x onerror=alert(1)>}'); ``` ### Impact MathLive users who render untrusted mathematical expressions can encounter malicious input that runs arbitrary JavaScript.

Source published

29 Jul 2026 17:21:26 UTC

Source modified

29 Jul 2026 17:41:44 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L

Publisher rating · MODERATE