What’s Vulnerable › Vulnerabilities

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

• Severity: low (CVSS 3.7 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-10-19 · updated 2026-10-26
• Weakness: CWE-400

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.

Affected products

• markdown-it: from 15.0.0, < 15.0.3; before 14.3.3

References

• 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
• https://github.com/markdown-it/markdown-it/security/advisories/GHSA-vfgh-jcmw-g37q

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