CVE-2026-71478
Medium
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.
SeverityMedium
CVSS6.1
Exploit probability—
ProductLeague/commonmark
PublishedAug 6, 2026
First seenAug 6, 2026
How to fix
Update
- league/commonmark2.9.0 or later
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| league/commonmarkPackagist | 1.5.0 ≤ v < 2.9.0 | 2.9.0 |
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