Description
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.
Published: 2026-08-06
Score: 6.1 Medium
EPSS: < 1% Very Low
KEV: No
Impact: n/a
Action: n/a
AI Analysis

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Remediation

No vendor fix or workaround currently provided.

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Tracking

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Advisories
Source ID Title
Github GHSA Github GHSA GHSA-29pj-957v-52mc league/commonmark: AttributesExtension href/src unsafe-link filter bypass via embedded control bytes
History

Fri, 07 Aug 2026 17:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'poc', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Fri, 07 Aug 2026 01:30:00 +0000

Type Values Removed Values Added
First Time appeared Thephpleague
Thephpleague commonmark
Vendors & Products Thephpleague
Thephpleague commonmark

Thu, 06 Aug 2026 22:15:00 +0000

Type Values Removed Values Added
Description 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.
Title league/commonmark: AttributesExtension href/src unsafe-link filter bypass via embedded control bytes
Weaknesses CWE-692
CWE-79
CWE-86
References
Metrics cvssV3_1

{'score': 6.1, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N'}


Subscriptions

Thephpleague Commonmark
cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published:

Updated: 2026-08-07T17:05:57.244Z

Reserved: 2026-08-06T19:56:23.724Z

Link: CVE-2026-71478

cve-icon Vulnrichment

Updated: 2026-08-07T17:05:41.139Z

cve-icon NVD

No data.

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-08-07T01:15:04Z

Weaknesses