---
id: CVE-2026-86429
title: >-
  The league/commonmark (thephpleague/commonmark) library in versions >= 1.5.0
  and < 2.9.1 contains quadratic parsing complexity in its SmartPunctExtension
  and AttributesExtension
summary: >-
  The league/commonmark (thephpleague/commonmark) library in versions >= 1.5.0
  and < 2.9.1 contains quadratic parsing complexity in its SmartPunctExtension
  and AttributesExtension. When either extension is explicitly registered on the
  Envi…
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'
cwe:
  - CWE-407
vendor: thephpleague
product: commonmark
affected:
  - 'commonmark >= 1.5.0, < 2.9.1'
patched:
  - commonmark 2.9.1
published: '2026-09-07'
updated: '2026-09-19'
sourceUpdated: '2026-09-19T15:17:06.363'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-86429'
references:
  - url: >-
      https://github.com/thephpleague/commonmark/security/advisories/GHSA-jjv6-8j6v-6j52
    label: disclosure@vulncheck.com
  - url: >-
      https://www.vulncheck.com/advisories/commonmark-before-2.9.1-denial-of-service-via-smartpunct-and-attributes
    label: disclosure@vulncheck.com
tags:
  - nvd
  - cve.org
epss: 0.00515
epssPercentile: 0.41405
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-09-18T17:41:52.780733Z'
ingestedAt: '2026-09-08T20:10:03.179Z'
---

## Overview

The league/commonmark (thephpleague/commonmark) library in versions >= 1.5.0 and < 2.9.1 contains quadratic parsing complexity in its SmartPunctExtension and AttributesExtension. When either extension is explicitly registered on the Environment (they are not enabled by default and are excluded from the standard CommonMark and GitHub-Flavored Markdown converters), an unauthenticated attacker can submit small, specially crafted Markdown documents — such as text alternating with unpaired quotes, contiguous runs of block-level attribute blocks, or repeated class attributes — to trigger disproportionate CPU consumption and cause a denial of service. Fixed in 2.9.1.

## Affected

- `commonmark >= 1.5.0, < 2.9.1`

## Remediation

Upgrade past the affected range:

- `commonmark 2.9.1`