league/commonmark: DisallowedRawHtml bypassed when a disallowed tag name ends the raw-HTML literal — GHSA-97JJ-33GV-5XF9

Summary

## Summary The `DisallowedRawHtml` extension does not escape a disallowed tag when the tag name is the last thing in the raw HTML. A Markdown line containing just `<script` is emitted unchanged, and the next block can supply its attributes. With the shipped GFM defaults this allows stored XSS by anyone who can post Markdown. ## Details `DisallowedRawHtmlRenderer` escapes tags with this regex: ```…

Timeline

Published by source

2026-09-30

Risk context

• Reported severity or threat level: medium.
• Reported CVSS score: 6.1 out of 10.
• Review exposure for the affected product or family: composer: league/commonmark.

Product

composer: league/commonmark

What to do

General, cautious steps (verify details in the official source):

• Review exposure and plan remediation based on risk and environment.
• Identify affected product versions in your inventory and verify whether you are impacted.
• Apply vendor patches/updates or recommended mitigations as soon as available.
• Read the official advisory for exact affected versions and remediation steps.

Official advisory

• Read the official source

Evidence and provenance

Canonical advisory ID

GHSA-97JJ-33GV-5XF9

Source

GitHub

Vendor

GitHub

Published by source

2026-09-30

Last source activity

2026-09-30

Curated by

hlukh.ch

Related advisories and connections

These advisories are connected by shared CVE, product, vendor, source, or time signals.