---
id: CVE-2026-71478
title: >-
  league/commonmark is a PHP library for parsing and rendering CommonMark
  Markdown
summary: >-
  league/commonmark is a PHP library for parsing and rendering CommonMark
  Markdown. From 1.5.0 until 2.9.0, the AttributesExtension's href and src
  unsafe-link filter can be bypassed by embedding control bytes, such as a tab,
  carriage retur…
severity: medium
cvss: 6.1
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N'
cwe:
  - CWE-79
  - CWE-86
  - CWE-692
vendor: league
product: league/commonmark
affected:
  - 'league/commonmark >= 1.5.0, <= 2.8.3'
patched:
  - league/commonmark 2.9.0
published: '2026-08-06'
updated: '2026-09-10'
sourceUpdated: '2026-09-10T20:41:33.140'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-71478'
references:
  - url: >-
      https://github.com/thephpleague/commonmark/commit/493a5aa7d65754b73846006eaff9c2c4431a8e2c
    label: security-advisories@github.com
  - url: 'https://github.com/thephpleague/commonmark/releases/tag/2.9.0'
    label: security-advisories@github.com
  - url: >-
      https://github.com/thephpleague/commonmark/security/advisories/GHSA-29pj-957v-52mc
    label: security-advisories@github.com
  - url: >-
      https://github.com/thephpleague/commonmark/security/advisories/GHSA-29pj-957v-52mc
    label: 134c704f-9b21-4f2e-91b3-4a467353bcc0
  - url: 'https://github.com/advisories/GHSA-29pj-957v-52mc'
tags:
  - nvd
  - ghsa
  - composer
epss: 0.00355
epssPercentile: 0.26448
aliases:
  - GHSA-29pj-957v-52mc
ecosystem: composer
ingestedAt: '2026-08-06T21:04:22.234Z'
---

## Overview

league/commonmark is a PHP library for parsing and rendering CommonMark Markdown. From 1.5.0 until 2.9.0, the AttributesExtension's href and src unsafe-link filter can be bypassed by embedding control bytes, such as a tab, carriage return, line feed, or leading C0 control character, in a javascript: URL that browsers discard before parsing the scheme, causing the browser to still execute the script even when the unsafe-link filter is enabled. This issue is fixed in 2.9.0.

## Remediation

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

## Package advisory (CVE-2026-71478)

Affected packages:

- `league/commonmark >= 1.5.0, <= 2.8.3`

Patched in:

- `league/commonmark 2.9.0`

Source: https://github.com/advisories/GHSA-29pj-957v-52mc