CVE-2026-30838
6.1 · MEDIUMOverview
CVE-2026-30838 is a medium-severity vulnerability affecting thephpleague commonmark. It was published on March 7, 2026 and has a CVSS 3.1 base score of 6.1 (MEDIUM).
This vulnerability has a CVSS 3.1 base score of 6.1, rated MEDIUM. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.
Technical Description
league/commonmark is a PHP Markdown parser. Prior to version 2.8.1, the DisallowedRawHtml extension can be bypassed by inserting a newline, tab, or other ASCII whitespace character between a disallowed HTML tag name and the closing >. For example, <script\n> would pass through unfiltered and be rendered as a valid HTML tag by browsers. This is a cross-site scripting (XSS) vector for any application that relies on this extension to sanitize untrusted user input. All applications using the DisallowedRawHtml extension to process untrusted markdown are affected. Applications that use a dedicated HTML sanitizer (such as HTML Purifier) on the rendered output are not affected. This issue has been patched in version 2.8.1.
Remediation
Check the references section for vendor advisories and patches from thephpleague. Update commonmark to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.
Affected Products
| Vendor | Product | Versions | Status |
|---|---|---|---|
| thephpleague | commonmark | >= 0, < 2.8.1 | Affected |
Frequently Asked Questions
What is CVE-2026-30838?
CVE-2026-30838 is a medium-severity vulnerability affecting thephpleague commonmark. It was published on March 7, 2026 and has a CVSS 3.1 base score of 6.1 (MEDIUM).
How severe is CVE-2026-30838?
This vulnerability has a CVSS 3.1 base score of 6.1, rated MEDIUM. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.
How do I fix or remediate CVE-2026-30838?
Check the references section for vendor advisories and patches from thephpleague. Update commonmark to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.
How can CyberStrike help with CVE-2026-30838?
CyberStrike's AI-powered security agents can automatically detect CVE-2026-30838 across your infrastructure using autonomous pentesting, DAST scanning, and HackBrowser. The platform continuously monitors for known vulnerabilities and provides actionable remediation guidance prioritized by real-world exploitability.
How CyberStrike Helps
AI agents map your attack surface to find vulnerabilities like this one.
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