markdown-it: Quadratic complexity in smartquotes with unmatched closing quotes

### Impact When `typographer: true` is enabled, specially crafted Markdown can cause quadratic processing time in the smartquotes rule, potentially leading to denial of service in applications processing untrusted input. Many opening double quotes followed by unmatched closing single quotes cause repeated scans of the entire opener stack. The same issue occurs with the quote types reversed. The default configuration (`typographer: false`) is not affected, but this option is enabled with high probability. ### Reproduction ```js import MarkdownIt from 'markdown-it' import { performance } from 'node:perf_hooks' const md = new MarkdownIt({ typographer: true }) for (const k of [2000, 4000, 8000, 16000, 32000]) { const input = '"a '.repeat(k) + "b' ".repeat(k) const start = performance.now() md.render(input) console.log(input.length, (performance.now() - start).toFixed(1), 'ms') } ``` Result: |input size|time| |-|-| |12000|18ms| |24000|47ms| |48000|115ms| |96000|428ms| |192000|1586ms| ### Patches Fixed in **15.0.2** and **14.3.2**. ### Workarounds Disable typography with `typographer: false`, or disable only the smartquotes rule: ```js md.disable('smartquotes') ```

Source published

20 Oct 2026 14:34:50 UTC

Source modified

20 Oct 2026 14:45:03 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:N/UI:N/S:U/C:N/I:N/A:H

Publisher rating · HIGH