CVE-2026-71478

league/commonmark: AttributesExtension href/src unsafe-link filter bypass via embedded control bytes

State: Published
Severity: 6.1 Medium
Published: Aug 6, 2026
Updated: Aug 7, 2026
Reserved: Aug 6, 2026

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.

Scores

CVSS	Score	Vector	Source
3.1	6.1 Medium	CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N	GitHub_M

Weaknesses

CWE-79 Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
CWE-86 Improper Neutralization of Invalid Characters in Identifiers in Web Pages
CWE-692 Incomplete Denylist to Cross-Site Scripting

Affected Products

Product	Versions
commonmarkthephpleague	>= 1.5.0, <= 2.8.3Affected

References

Every record here comes from the CVE Program’s CVE List. © 1999–2026 The MITRE Corporation. CVE is a registered trademark of The MITRE Corporation. The records are reproduced under the CVE Program terms of use.