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Vulnerabilities

Vulnerability · CVE-2026-111766

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

Published Oct 20, 2026 · catalog updated Oct 20, 2026 · markdown-it: Quadratic-time denial of

Last checked Nov 3, 2026. A connected source was read within the last 7 days.

Check if you run it

No confirmed exploitation is on record for CVE-2026-111766. EPSS is 0.43%. Act only if a listed version of markdown-it: Quadratic-time denial of is installed.

Gaps on this record

  • The stored product name is a package slug. The name on this page is taken from the title (markdown-it: Quadratic-time denial of).
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
Low3.7
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.43%
Remediation
Version ranges on file
Affected products
npm markdown-it

### Summary With , markdown-it takes quadratic time to parse repeated unterminated HTML constructs inside a paragraph. This affects HTML comments ( ), processing instructions ( ), declarations ( ), and CDATA sections ( ). An attacker-controlled input of a few hundred kilobytes can block the Node.js event loop for seconds or tens of seconds. The default configuration has HTML disabled, but the preset enables it. The issue was reported against the published package on Node.js 20 and reproduced on the current source with Node.js 24.16.0. ### Details treats as a terminator, causing the inline parser to attempt the HTML rule at successive HTML construct openers. With HTML enabled, applies an anchored regular expression to the remaining input: The comment, processing instruction, declaration, and CDATA alternatives in scan the remaining input for their respective terminators: , , , and . When the terminator is absent, matching fails. Parsing eventually reaches the next opener and scans an overlapping suffix again. Repeating this across the paragraph produces quadratic total work. For these inputs, the problem is repeated scanning across separate matches. The payload must reach inline parsing. Prefixing it with keeps it inside a paragraph. Starting a line directly with one of these constructs instead invokes HTML block parsing, which does not exhibit the same repeated inline scans for these payloads. The existing test in already contains a reproducer: However, it runs with default options, where HTML is disabled. A fix should avoid repeated searches for absent terminators across all four affected alternatives, for example by caching failed searches on the inline state. Fixing only the comment alternative leaves the other three cases affected. Regression coverage should exercise all four with . The original report was submitted by [@JarLob](https://github.com/JarLob). It credits the [GitHub Security Lab Taskflow Agent](https://github.com/GitHubSecurityLab/seclab-taskflow-ag

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • npm markdown-it< 14.3.3
  • npm markdown-it>= 15.0.0, < 15.0.3

How to fix CVE-2026-111766

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-111766. EPSS is 0.43%. Act only if a listed version of markdown-it: Quadratic-time denial of is installed.

Which versions are affected?

Compare what you have installed with < 14.3.3, >= 15.0.0, < 15.0.3. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-400: Uncontrolled Resource Consumption; CWE-407. EPSS 0.43%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Oct 20, 2026 · GitHub Advisory Database

    Detected

    ### Summary With , markdown-it takes quadratic time to parse repeated unterminated HTML constructs inside a paragraph. This affects HTML comments ( ), processing instructions ( ), declarations ( ), and CDATA sections ( ). An attacker-controlled input of a few hundred kilobytes can block the Node.js event loop for seconds or tens of seconds. The default configuration has HTML disabled, but the pres

  2. Oct 20, 2026 · GitHub Advisory Database

    Updated

    ### Summary With , markdown-it takes quadratic time to parse repeated unterminated HTML constructs inside a paragraph. This affects HTML comments ( ), processing instructions ( ), declarations ( ), and CDATA sections ( ). An attacker-controlled input of a few hundred kilobytes can block the Node.js event loop for seconds or tens of seconds. The default configuration has HTML disabled, but the pres

Sources

References

Freshness

Last verified in this catalog Nov 3, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.

  • FIRST EPSSNov 3, 2026
  • CVE.orgOct 22, 2026
  • GitHub Advisory DatabaseOct 21, 2026