Cross-Site Scripting Vulnerability in league/commonmark PHP Markdown Parser
CVE-2026-30838

5.1MEDIUM

Key Information:

Vendor

ThePHPleague

Status
Commonmark
Vendor
CVE Published:
7 March 2026

What is CVE-2026-30838?

The league/commonmark PHP Markdown parser is susceptible to a cross-site scripting (XSS) vulnerability due to a flaw in the DisallowedRawHtml extension. Attackers can exploit this weakness by inserting whitespace characters between disallowed HTML tag names and the closing >, allowing malicious scripts to bypass filters and be executed by browsers. This presents a significant risk for applications relying on this extension to handle untrusted input. Users are urged to upgrade to version 2.8.1 or later, or implement a dedicated HTML sanitizer such as HTML Purifier to mitigate the risk.

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Affected Version(s)

commonmark < 2.8.1

References

https://github.com/thephpleague/commonmark/security/advis...
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CVSS V4

Score:
5.1
Severity:
MEDIUM
Confidentiality:
None
Integrity:
Low
Availability:
None
Attack Vector:
Network
Attack Complexity:
Low
Attack Required:
None
Privileges Required:
Undefined
User Interaction:
Unknown

Timeline

  • Vulnerability published

  • Vulnerability Reserved

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