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.
References5
- github.com/markdown-it/markdown-it/commit/928bc8c11ded60181c0e7…
- github.com/markdown-it/markdown-it/commit/d99f48839d37af6fd8a26…
- github.com/markdown-it/markdown-it/releases/tag/14.3.3
- github.com/markdown-it/markdown-it/releases/tag/15.0.3
- github.com/markdown-it/markdown-it/security/advisories/GHSA-vfg…
Metrics
- CVSS 3.1
-
3.7
LOW
Score source: CNA
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L - EPSS — exploit probability
- 0% percentile: 37 · as of 10 November 2026
- CWE
- CWE-400CWE-407
Could this be exploited in your environment?
A patch closes the known hole. A penetration test shows what an attacker can still reach — with proof.