CVE-2026-71478

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.

CVSS 3.1

6.1CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

EPSS

0.4% chance of exploitation in the next 30 days; higher than 28% of CVEs (scores of 2026-10-25)

CWEs

CWE-79, CWE-86, CWE-692

Published

2026-08-06

Modified

2026-10-24

Record from

the NVD, synced 2026-10-24

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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