ApostropheCMS is an open-source Node.js content management system. In sanitize-html 2.18.0, when an <iframe> is not allowed and disallowedTagsMode is 'discard' (the defaults), its raw-text content is re-sanitized by a recursive call to sanitizeHtml(text, options). The recursion has no bound and starts each nested call with a fresh state. This vulnerability is fixed in 2.18.1.

Affected: npm: sanitize-html

### Summary

Since 2.18.0, when an `<iframe>` is not allowed and `disallowedTagsMode` is `'discard'` (the defaults), its raw-text content is re-sanitized by a recursive call to `sanitizeHtml(text, options)` (the change from #5564, fixing #5550). The recursion has no bound and starts each nested call with a fresh state. Two consequences, both absent from 2.17.7 and 2.17.4:

1. A few kilobytes of unclosed `<iframe>` tags throw `RangeError: Maximum call stack size exceeded` with the default options. Any application that sanitizes untrusted HTML with 2.18.0 can be made to throw on a small crafted input. 2. `nestingLimit` is not enforced across a discarded iframe: each nested iframe restarts the depth count at zero, so the output can be nested arbitrarily deep regardless of the configured limit.

### Affected versions

- 2.18.0 (the current `latest`), and the `main` branch at the time of writing (the recursive call is still in `packages/sanitize-html/index.js`, in the `ontext` handler, branch `tag === 'iframe' && !tagAllowed(tag) && options.disallowedTagsMode === 'discard'`). - Not affected: 2.17.7 and 2.17.4 (tested with the same inputs below).

Tested with Node.js v26.7.0.

### Reproduction 1: stack overflow with the default options

```js const sanitizeHtml = require('sanitize-html');

// with 2.18.0: sanitizeHtml('<iframe>'.repeat(1000)); // 8,000 chars: returns '' sanitizeHtml('<iframe>'.repeat(2000)); // 16,000 chars: throws RangeError: Maximum call stack siz…