---
id: CVE-2026-86433
title: >-
  commonmark versions from 1.5.0 before 2.8.4 contain a denial of service
  vulnerability in the Attributes extension where
  AttributesListener::findTargetAndDirection() performs quadratic-time sibling
  list scanning
summary: >-
  commonmark versions from 1.5.0 before 2.8.4 contain a denial of service
  vulnerability in the Attributes extension where
  AttributesListener::findTargetAndDirection() performs quadratic-time sibling
  list scanning. Unauthenticated attackers…
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 < 2.8.4
published: '2026-09-07'
updated: '2026-09-08'
sourceUpdated: '2026-09-08T19:57:49.663'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-86433'
references:
  - url: >-
      https://github.com/thephpleague/commonmark/security/advisories/GHSA-g2gp-3wwq-f4ph
    label: disclosure@vulncheck.com
  - url: >-
      https://www.vulncheck.com/advisories/commonmark-1.5.0-before-2.8.4-denial-of-service-via-attributes
    label: disclosure@vulncheck.com
tags:
  - nvd
  - cve.org
epss: 0.00509
epssPercentile: 0.40975
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-09-08T12:50:12.374530Z'
ingestedAt: '2026-09-08T15:33:26.977Z'
---

## Overview

commonmark versions from 1.5.0 before 2.8.4 contain a denial of service vulnerability in the Attributes extension where AttributesListener::findTargetAndDirection() performs quadratic-time sibling list scanning. Unauthenticated attackers can submit approximately 32 KB of repeated attribute blocks to cause parsing to take over 5 seconds, exhausting server resources.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.