What’s Vulnerable › Vulnerabilities

CVE-2026-71478: league/commonmark: AttributesExtension href/src unsafe-link filter bypass via embedded control bytes

• Severity: medium (CVSS 6.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-08-06 · updated 2026-10-24
• Weakness: CWE-79

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.

Affected products

• thephpleague commonmark: from 1.5.0, <= 2.8.3

References

• https://github.com/thephpleague/commonmark/commit/493a5aa7d65754b73846006eaff9c2c4431a8e2c
• https://github.com/thephpleague/commonmark/releases/tag/2.9.0
• https://github.com/thephpleague/commonmark/security/advisories/GHSA-29pj-957v-52mc
• https://github.com/thephpleague/commonmark/security/advisories/GHSA-29pj-957v-52mc

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