CVE-2026-71478 Details
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.
A cross-site scripting vulnerability has been identified in the League CommonMark PHP library, specifically in versions 1.5.0 prior to 2.9.0. The issue arises within the AttributesExtension, where the href and src unsafe-link filter can be bypassed. This is achieved by embedding control bytes, such as tabs or line feeds, into a javascript: URL. Browsers discard these control bytes before processing the URL, allowing the embedded script to execute even with the unsafe-link filter active. The vulnerability is present because the filter's regex does not account for these obfuscation techniques, enabling the execution of scripts through manipulated links.
Users can upgrade to League CommonMark version 2.9.0 or later, where this vulnerability has been fixed.
Metrics
CVSS 4.0 Severity and Vector Strings:
No CVSS 4.0 data is available for this CVE.
CVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
CISA-ADP
Assessed Aug 7, 2026References to Advisories, Solutions, and Tools
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Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-692 | Incomplete Denylist to Cross-Site Scripting | [email protected] |
| CWE-79 | Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') | [email protected] |
| CWE-86 | Improper Neutralization of Invalid Characters in Identifiers in Web Pages | [email protected] |
Affected Products
No affected product data is available for this CVE.
Change History
2 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Aug 7, 2026 | CVE Modified | CISA-ADP |
| Aug 6, 2026 | New CVE Received | [email protected] |