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[ CVE-2026-111766 · Published 19 Oct 2026 ]

markdown-it: Quadratic-time denial of service in inline HTML parsing with html enabled

CVSS 3.7 EPSS <1%Fix available

[ Description ]Official description

markdown-it is a Markdown parser. Prior to 14.3.3 and 15.0.3, when the html option or commonmark preset is enabled and the constructs occur inside a paragraph, attacker-controlled Markdown containing repeated unterminated inline HTML comments, processing instructions, declarations, or CDATA sections reaches src/rules_inline/html_inline.ts. Its HTML_TAG_RE match searches the remaining suffix for the appropriate terminator; when no terminator is present, parsing advances to the next opener and repeats the match over overlapping input, causing quadratic processing and denial of service through event-loop blocking or an unresponsive browser main thread. HTML blocks and the default HTML-disabled configuration are not affected by these payloads. This issue is fixed in versions 14.3.3 and 15.0.3.

[ Fixes ]Fixes and patches

  • markdown-it 14.3.3Fixed version · GitHub Advisories · npm package markdown-it: upgrade to 14.3.3 or later (affected < 14.3.3)
  • markdown-it 15.0.3Fixed version · GitHub Advisories · npm package markdown-it: upgrade to 15.0.3 or later (affected >= 15.0.0, < 15.0.3)

[ Packages ]Affected open-source packages

[ References ]References