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

> Attackers can cause denial of service via quadratic-time processing in markdown-it when HTML parsing is enabled, blocking the event loop or browser thread.

- **Severity:** Low 3.7 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 19 Oct 2026
- **Updated:** 26 Oct 2026
- **Also known as:** CLSA-2026-1793097495, CLSA-2026-1793097603, CLSA-2026-1793099982, CLSA-2026-1793100014, CLSA-2026-1793125795, DEBIAN-CVE-2026-111766, ECHO-9559-b172-500b, GHSA-vfgh-jcmw-g37q, UBUNTU-CVE-2026-111766

## What is CVE-2026-111766?

CVE-2026-111766 is a low-severity denial of service vulnerability in markdown-it, published on 19 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-407 (Inefficient Algorithmic Complexity), CWE-400 (Uncontrolled Resource Consumption)

## Which versions are affected by CVE-2026-111766?

4 open source packages ship an affected version, including markdown-it.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `markdown-it` | npm | All versions | 14.3.3 |
| `markdown-it` | npm | All versions | 14.3.3 |
| `markdown-it` | npm | From 15.0.0 | 15.0.3 |
| `markdown-it` | npm | From 15.0.0 | 15.0.3 |

## How do I fix CVE-2026-111766?

Upgrade markdown-it to a fixed version for your release line: 14.3.3 or 15.0.3.

## Is CVE-2026-111766 being exploited?

There is no known exploitation of CVE-2026-111766 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-111766 and fix it if it is affected.

What it is: CVE-2026-111766 is a low-severity denial of service vulnerability in markdown-it, published on 19 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-111766 in the wild and no public exploit code.

Affected packages and fixed versions:
- markdown-it (npm): affected all versions; fixed in 14.3.3
- markdown-it (npm): affected all versions; fixed in 14.3.3
- markdown-it (npm): affected from 15.0.0; fixed in 15.0.3
- markdown-it (npm): affected from 15.0.0; fixed in 15.0.3

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-111766/ (Markdown: https://insights.sbomify.com/CVE-2026-111766/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-111766
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-111766
- OSV: https://osv.dev/vulnerability/CVE-2026-111766

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-111766/
Summaries are generated and may contain mistakes; the official description above is the record.