CVE-2026-111759

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

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')
}

md.disable('smartquotes')

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.

Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service. Typical impact: denial of service.

CVE-2026-111759 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (15.0.2, 14.3.2); upgrading removes the vulnerable code path.

Kodem intelligence

Already deployed Kodem?

Fixed in 15.0.2 and 14.3.2.

1. What is CVE-2026-111759? CVE-2026-111759 is a high-severity uncontrolled resource consumption vulnerability in markdown-it (npm), affecting versions >= 15.0.0, < 15.0.2. It is fixed in 15.0.2, 14.3.2. Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service.
2. How severe is CVE-2026-111759? CVE-2026-111759 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of markdown-it are affected by CVE-2026-111759? markdown-it (npm) versions >= 15.0.0, < 15.0.2 is affected.
4. Is there a fix for CVE-2026-111759? Yes. CVE-2026-111759 is fixed in 15.0.2, 14.3.2. Upgrade to this version or later.
5. Is CVE-2026-111759 exploitable, and should I be worried? Whether CVE-2026-111759 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-111759 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-111759?
   • Upgrade markdown-it to 15.0.2 or later
   • Upgrade markdown-it to 14.3.2 or later

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